Comment by NoGravitas

> It loses about 5 minutes a day

This suggests it's completely out of spec, and maybe beyond saving. However, regulating functioning Seiko movements is certainly within reach for enthusiasts using a timegrapher device, or software with a microphone. Persistently adjusting over a few days, it should be able to get within -10,+10 seconds per day.

The timegrapher will also reveal the condition of the movement and whether further work is worthwhile. Servicing these movements is likely more expensive than replacing them.

It's not hard to make the adjustment, but you need a timegrapher to measure the results in a reasonable time.

I've adjusted a couple of my watches over the course of a week or two by making small adjustments, noting the time, wearing it for a day, and then noting how much the time had changed versus a "known good" time. It's a pain but doable.

There are mobile apps that use the phone's microphone to measure the watch's "ticks" and graph them for you. They aren't anywhere near as accurate as a "real" timegrapher but they'll get you close enough.

At one point I had about a dozen mechanical watches. These days I have three, and only one that I wear almost exclusively. It's a Maratac Mid-Pilot, which uses a Miyota 8245 movement. I've used the "adjust and check later" method to adjust it, and it loses about 10s per week - well within the acceptable range.

The other two that I've kept are a Seagull 1963, which I wear as a "dress watch", and a Vostok Retro 1934, which I sometimes wear when I want a change of pace. It has a white face and I have a variety of brightly-colored straps for it.

One day I'll step up and buy a Hamilton, but I'm still savoring the serotonin from looking at them and anticipating :).