You might not like this answer:
find a better case back from a donor watch or an entire better case from a donor watch
I have an old ladies' pendant watch with a pitted case back.
The metal was always thin to begin with, but there are several small spots where the metal is corroded right through.
The holes are small and I was thinking about covering them with soft solder- but the case is gold-filled, and the solder would not match.
I have never seen this problem before, and I have no idea how to fix it.
What is the usual remedy for this kind of problem?
You might not like this answer:
find a better case back from a donor watch or an entire better case from a donor watch
I always hate seeing case damage repaired with soft solder. It tends to run and leaves a mess and the tarnished solder is plain ugly. If this is a watch you care about, take the time to learn to silver solder. There are videos on the internet that will show you the basics. There are even yellow colored alloys that will look OK when polished. They wear well but of course will tarnish fairly quickly. Working from the inside of the case, you can close up most holes without making the outside any worse. You may have to do some filing to get clearance back for the movement. Joel