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Seiko Marine Master "MM300" Blue SLA023J1

November 26, 2019

Quite recently (around mid this year), I experienced a slight fatigue with Seiko and its recent releases. I looked around to own another watch for a change and found a formidable and lovable piece in Oris’ Divers 65 in 40mm in which I thoroughly reviewed here. I guess as I looked around for another brand; I missed the feeling of looking into Seiko the same way I did for my latest Oris piece.

As I wished Seiko would release something that would captivate me back into the brand’s loving arms, I guess the Japanese watch giant heard me, in one way or another, and released the new Marine Master 300 SLA023J1.

Oh boy, was I back in love with Seiko more than ever! Let me show you why this may be one of the best modern divers at the price range.

Look and Feel

Before I start to discuss how the watch looks and feels, I want to tell you how I got the watch and its interesting political back story.

So, I was just in Hongkong recently for a quick trip. The timing was in question and a concern since a lot of political noise and turmoil is happening in one of my favorite Asian cities.  When I was there, most of the stores around the Tsim Sha Tsui – Nathan Road area are closed and that worried me. Good thing was that my favorite Seiko AD was open and had the SLA023J1 on display.

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The TST MTR Station near my hotel is blocked and barricaded at the height of the protests

The SLA023J1 MM300 sang to me and I immediately decided to bring it home. While I was going back to my hotel that night, the protests have escalated to the point that all mass transports were halted, streets are blocked/vandalized, and you can smell the faint smell of tear gas in the air. So, looking at the SLA023J1 MM300 today continually reminds me of my unique and surreal experience in Hongkong during the protest riots of November 2019.

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The SLA023J1 is a constant reminder of my experience in HK during the protests

Anyways, the immediate factor that the SLA023J1 had which stood out for me was its attractive deep blue sub burst dial. I like the color tones used by Seiko this time as at certain angles, the dial seems to be black in color but in certain lighting conditions, you can really see its magnificent deep blue colorway.

The round applied indices are still very particular to the MM300 heritage. Same goes with the date window and hands (hours, minutes, and seconds) which still reflects the same placements and design from the previous MM300 models. Although, one very particular difference in the newer MM300 models nowadays compared to the previous model (SBDX017) is the lack of the “Marine Master” text. This is now replaced with the Prospex logo. Personally, it was a bummer but the other improvements that is brought in by the new MM300 models seemingly make up for it.


The SLA023J1's crown is stamped with the Prospex logo


Certain lighting conditions turns its deep blue dial  closer to a black colorway

The SLA023J1 MM300 now sports an anti-reflective coated sapphire glass that was frequently yearned by earlier MM300 model owners. Also, the blue MM300 packs a ceramic bezel that is more fitting for a watch of this price and stature.


However, you would immediately notice the lack of the 12’o’clock pip which was a hallmark from the SBDX017 and earlier MM300 models. In place is a reverse triangle lume marking on the 12’o’clock bezel position. Its quite a bit odd though since the lume on the reverse triangle marking seems to be exposed. You can actually feel the roughness of the lume with your fingers. For SLA019J1, SLA021J1 and SLA023J1 owners, do you have the same experience?


Seiko still uses the same metal bracelet from the previous MM300 models

The Seiko SLA023J1’s case size is no different from the previous generation MM300 with a diameter of 44.3mm and case thickness of 15.4mm. A lot of potential buyers would shy away with the 44.3mm case size tidbit but initial wearers would attest that the MM300 would wear similarly on the wrist like a 42mm diver due to its low center of gravity and excellent weight distribution.

The Blue MM300 SLA023J1’s metal bracelet is still the same as the previous models. It still contains a combination of polished and brushed metal parts that is coated with Seiko’s Diashield technology to help withstand minor bumps and scratches. The same unique diver’s extension can be found and extended by lifting the clasp lock. A future personal upgrade for me is to install a jubilee bracelet from Strapcode.


The MM300's diver's extension sitting below the clasp

Out of the box, the blue MM300 comes standard with a separate black rubber strap that is quite comfortable. Although, I wish they kept the black waffle rubber strap that was found in previous generation MM300 sets. Pairing the MM300 with the black waffler rubber strap is just not for the looks department but its to maintain the iconic heritage of the Seiko MM300 diver that we’ve all known and loved.  


One of the major selling points for me to get the SLA023J1 is its movement. The blue MM300 packs the legendary 8L35B automatic movement which holds about 50 hours power reserve and comes with 26 jewels. With the MM300’s usage of a monobloc case (meaning no physical removable case back), the watch can easily attain its 300M water resistance metric.

It is often told that the 8L35B is very similar to Grand Seiko’s 9S55 automatic movement. The only difference is that the later (GS 9S55) is calibrated and adjusted to meet its advertised specifications wherein the 8L35B is a close cousin base movement.

Even though the 8L35B is compared to an uncalibrated 9S55, it still provides reliable accuracy and toughness which is all you need really for a diver’s watch.


The Seiko SLA023J1 Blue MM300 pricing should hover between $2800 to $3200 USD as of this posting. This is expected and typical of any non-limited or non-special edition MM300 watch release from Seiko.

I would expect it to hold value when new but loose about 10-15% of the MSRP when sold if its slightly used. But due to the watch being so beautiful in blue, there might be some early hype that could push the watch’s MSRP a little bit more.


The Seiko SLA023J1's monobloc case for a more effective water resistance


The Seiko SLA023J1 MM300 in full set


Well what can I say; this Seiko Blue MM300 is a real stunner!

The magnificent blue dial and ceramic bezel easily catches the eyes of both WIS and Non-WIS friends and colleagues. I’ve separately gotten a complement on how shiny my watch is and its probably due to the Seiko Zaratsu polishing of the watch case’s side to a mirror finish.

Some of my watch snob friends didn’t quite understand why I paid more than $2000 USD for a Seiko. But once they saw and held it in person, they are now truly appreciative of the Seiko Marine Master and its spectacular build quality. I guess I opened their eyes and look beyond what Rolex, Omega, etc. can offer.

But real WIS will truly understand, appreciate, and love Seiko as a brand. Regardless of which model and line-up, Seiko is a natural choice if you are looking for watches with in-house movements. Seiko and Grand Seiko is now considered a global watch maker powerhouse that can rival some of the mightiest brands of the Swiss and real WIS know that by heart.

But what If I already own the previous generation Seiko Marine Master MM300, will I still buy it?

It’s a YES if:

  • You want a clean blue version of the SLA021 or SBDX017

  • You want a blue version of the MM300 but is not willing to pay the premium of limited-edition models released previously (Thai Limited Ed.)

It’s a NO if:

  • You are satisfied with having one MM300

  • You still want your MM300 sporting the “Marine Master” text on the dial

If I do see another person wearing this watch, it tells me the following:

  • Appreciates Seiko as a brand and its offerings at the price range

  • Truly understand Horology and Heritage of timepieces

Watch Daddy Rating


  • Upgraded to now use an anti-reflective sapphire crystal and ceramic bezel

  • Top notch and desired usage of Seiko’s Caliber 8L35B

  • One of the most iconic diver’s watches to date

  • Classy and Beautiful blue colorway that fits most occasions


  • Still uses an outdated bracelet design which can be improved

  • Extra black rubber strap should have been a waffle style design

  • Lack of the “Marine Master” text to symbolize its heritage and iconic stature

Highly Recommended

Watch Daddy Picks


Seiko MM300 Blue SLA023J1

  • Seiko Caliber 8L35 movement (-10/+15 seconds a day) with Hacking and Hand Winding

  • Stainless Steel Case and bracelet with Diashield coating

  • Sapphire Crystal Glass

  • Ceramic Bezel

  • Case Size: 44.3mm with 20mm lug size

  • Water Resistant - 300 M

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