Vintage Omega Seamaster 600 & Geneve Automatic

Recently, I purchased these two vintage Omegas for a price of about 500 euros.

The first is a stainless steel 1968 (let me know if I'm wrong here) Omega Seamaster 600 Date (ref. 135.012 according to the case back) in working condition. It has quite a lot of scratches on the crystal, which, in my unprofessional opinion, is not original. However, I don't have any equipment to have a better look. Caliber 601 and diameter 32mm.

The second piece is a gold-plated 1971 Omega Geneve Automatic Date, ref. 166.070. Also working, though the minute hand catches the second hand, and doesn't let one move further, so definitely has to be fixed. Also, the crown seems to be odd. Though you can see some sort of Omega mark, I'm pretty sure it's not from the original watch. It also states "20" on the case, which I assume is related to the gold plating. Can anyone explain that to me, please?

My main priority is to wear and enjoy them, so I'd like to invest some money in restoration, but I also chatted with the local Omega official distributors, and they ask way too much. Any suggestions on what I should do?

New crystal on both. New crown on the gold one. I've never bought a watch with brassing like that, but if I had a gold one I would be tempted to try one of the home gold plating kits on it. The finish may not last, but you can always redo it.
And of course service as necessary.

Polywatched both crystals and the result seems to be quite satisfying. There are still some deeper scratches but it's better than it was for sure. The Seamaster's crystal appeared to be original with the Omega sign in the middle.

Yesterday I went to the local watch repair shop, which hasn't done any servicing except for changing caseback gaskets and cleaning the leftovers from the previous ones. After an hour, the Seamaster stopped working. I came back, he opened it, checked, and it started to work again. Now, after around 16 hours, it stopped again and doesn't seem to work anymore. What happened?