When I was a kid, my uncle had a number of old doubles and if they had pits, he would fill them with clear nail polish.
They would hold up for a session or two before dislodging.
Then, clean the chamber with remover and fill them again.
I never watched him do it so I'm not sure if he used a waxed case to smooth the polish or what.

I have wondered if a nickasil plating would work.
Hard as hell and can only be polished with diamond I think.
It's used for replating two stroke cylinders mostly as far as I know.