Hi All,
When I first got my Polysix, it had a bunch of dead keys (thank you eBay). I fixed them the same way that I fixed the dead keys on my Mono/Poly...with a daub of CaiKote for each key contact. It worked great!
But, now that it's been a few years, the keys on my Mono/Poly stopped working. Luckily, though, LA Synth Co started selling new key contacts for the Mono/Poly, Polysix, and other synths of that era. I bought a set for the Mono/Poly and installed them. They work great!
If you're interested, you can check out the replacement process at the link below. As the Polysix and Mono/Poly have the same type of keybed / key contacts, the process would be the same.
http://synthhacker.blogspot.com/2016/02/replacing-key-contacts-on-korg-monopoly.html
It's so fantastic that they've made these pieces available again. I don't know how they're getting them made, but it's a great service.
Chip