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I guess you are trying to send a picture of your hardware,but all I get is a 214 byte piece of trim like thing. No matter, those of us in the biz know what you are talking about.
? ?I had the occasion to work with these radios for about 5 years,and I didn't encounter the tin whisker that others seem to have, but I had quantities of adjusting cap screws that would corrode in their bores and cause themselves to loose a DC ground ..thus making a few PF cap- as it approached the top of the helical coil within the cavity- to become more like a piece of plastic .?
? ? Most of the time you could just give the screws a short twist -with accompanying sound of a small crack sound - which would suddenly boost your RX sens at least 10db at a time. I don't think I ever found more than 2 screws at a given time exhibiting the symptoms,but it happened to almost all of our ~350? VHF mobiles ..and in other UHF services the same thing occurred.
? ? Purely a metallurgical problem - RCA's and I think Johnsons of that day had a similar cavity configuration but were made of different metal alloy and adjusted slightly differently ..exhibiting no such problems.
? ? GE contracted with the Ben F. Nye company from Mas. or Con. or somewhere up East, that made stuff called NYOGEL. A version was the cure for corrosion of control head pin to socket problems ,but the black slurry that was for the cavity problem usually permanently cleared the stuck screw syndrome.?
? That screw grease was laced with micro grit of something sufficiently metal to clear and then bridge the screw thread gaps into the casting, and made a very good ground for the screw to casting surfaces.
? ?This stuff was like printer's ink as to how badly it stuck to anything it touched ,staining hands for a long time -unless you had GOOP or some commercial pumice based hand cleaner to get it off with.
? ? I have successfully used NO-Al-Ox -from ACE hardware or other electricians supply outlet as a replacement for NYOGEL.?
? ? ?As for a replacement casting, I doubt that you will find any new ones anywhere.
? ? ?The replacement castings were characterized by not having as bright a chromed look to them,but otherwise appeared identical.
? ? ? As to the tin whiskers, I have heard of guys running a Q tip around inside the cavity to snag them, and then using some kind of cleaner /anti corrosive as a chaser. I never had that problem sufficient to be conversant in the specifics. As we were? a LEO /local Gov't shop, with future sales in the works, we were quickly enrolled in the One for One swapout as needed Club by GE.
? ? ? ?Subsequent radio models abandoned that exact kind of cavity system, thank Pee Wee Herman.
? ? ? The cavities are pretty easy to pull apart ,but I'd recommend you try the grease first (just run the screw out all the way and apply the grease sparingly as you run it back in and out a few times to really coat the threads.
? ? ? Peak? the cavity and move on.
? ? ? If you can't get the whole thing down to below 1uv ,it's time for a tear down and de whisker. If still too low, it's probably time for a Witch Doctor.
? ? ? I have no memory of the part number for the better castings,and suspect that they are automatically registered as obsolete and crossed to the newer part number ...IF even still shown.?

Lots of Luck.

DWF
Pinellas CO. Sheriff's Dept Ret.2009