Sliding rear window woes...

[HIGHWAY BY THE SEA]

I just bought a sliding glass window assembly that came out of a 1976 C10. The first thing I noticed is that the rubber gaskets and felt linings in it are all old and deteriorated. Those things seem to be impossible to find replacements for. The other problem is when I attempted to remove the two black pieces of the broken plastic window lock to install my brand new one made of metal, the screws on one of them broke off in the window. I hate to have to drill out the screws because they are rusted into the aluminum. The screws got wet and rusted into the aluminum with oxidation. Does anyone know where to find decent replacement rubber and felt linings? I may also need to find the metal piece that attaches to the window to avoid drilling out those screws.