Tuning Capacitor works after cleaning, but goes out again!

[Magnavox300]

Just redid this 1960 GE Musaphonic radio... put in new caps, and resistors as needed. When switched to the phono input, an iPod works clear and perfect, but the radio could not get any stations for the AM.... just crackling and all static... I sprayed the tuning capacitor with Deox, then stations came in clear... after a few minutes went out... cleaned it again with 90% alcohol, stations came in even better, no crackling or popping at all, but after a few minutes, went out again...
still just static and crackling.... wondering why??

[init4fun]

A couple of things I'd check;

First, are you 101% sure none of the variable capacitor's plates are hitting each other? The solvent could be keeping them electrically apart till it dries.

On the flip side, have you checked for bad solder connections where the tuning cap mounts to the board? Perhaps the solvent is bridging an open solder joint till it dries?

Could the solvent be increasing or decreasing the capacitance of the trimmer caps mounted on top of the tuning gang ?

[damen]

Sounds like silver mica disease (SMD) in the IF transformers. Those GEs are notorious for that problem. Many videos on how to repair.

[Electronic M]

Another possibility is something akin to tin whiskers or very fine metal in the plates. Sometimes following up the cleaner by sliding a piece of copy paper between each plate gap to clean out the junk between them will do what cleaner alone can't.