I bought a Seiko 2J31-001A as a gift to someone.

The watch's exterior looked pristine but inside there were signs of battery leak.

After cleaning the residues of the leak and dropped in a rather hard-to-find SR421SW battery, the second hand twitched in place — not that it was broadcasting a livestream but it didn't advance normally.

Well, simple, it needs a simple disassembly and clean.

But not so simple with a watch this small and having absolutely tiny Phillips screws for the purpose of, I don't know, tamper prevention?

My Ph00000 tip didn't work because its pointed end was too long. My flat head can fit in but not deep enough to gain traction.

Luckily online people had an idea to sand down the tip of a flat head to a shape between V and U, then I was able to unscrew the 2 Phillips screws.

While the technical guide isn't available online, I found a blog post with some useful photos of the interior which I can use to plan my moves.

……?

Oh what's this? Is this a dangling clutch wheel that is not gonna come back and bite me?

So carefully I proceeded with the disassembly, up until I had access to both the top and bottom jewels of the wheels except the minute wheel, which I predict my attempt to remove will likely crush the tiny pinion with tools that I have.

I used a toothpick with IPA and rodico to clean the jewel bearings through the gaps of the bridges still installed on the movement.

The cups of the jewels were installed towards the pinions so it was pretty easy to install the wheel plate.

Then, after having installed the dial and hands, I tried to finish it all up by installing the stem, but the stem wouldn't go in.

I probably have tried and failed too many times to push the stem in. Fortunately this movement allows access to the keyless works without removing the dial and hands.

Yeah yeah ok, the clutch wheel was standing in the stem channel so I had to remove a few parts of the keyless works — without having to touch the wheels — to reposition it.

After that, the stem clicked right in. All good now.

For anyone who will work with a 2J31, I hope this post helps, as it's something I would have wanted before I gingerly opened it up.