Last year I purchased a CoCo 3 and accessories and thrown in with the package were two other CoCo 3’s that were “not working”. One of them had a poorly seated GIME chip and the other had a really crusty power switch. I was able to get both working with a bit of fiddling but the power switch was just never going to be quite right.
Luckily with the help of the community on the CoCo mailing list I was able to source a replacement switch. It was successfully installed and works perfectly. Here is a link to the switch: