Many years ago I was told by a Motorola 2 way tech their method of cleaning really cruddy chassis.
He took them home and put them in the dishwasher. (I suspect his wife was less than excited about that
First all the tubes, speaker, dynamotors, electrolytic caps, coils, IFT's, transformers and pots were removed. They would be replaced with new parts, or cleaned and reinstalled .
He said the key was to be sure the chassis was TOTALLY and COMPLETELY dry. He noted that he could "bake" them in the oven for a few hours at 200 deg. F. to be sure they were totally dry.
Variable caps were then lubricated with a drop of oil (ATF works fine as does electronic organ oil) on the bearings, then transformers, IFT's, etc were reinstalled, but all 'lytics were replaced, resistors checked for value and fixed capacitors were replaced as needed.
Radios were then re-aligned, tested for operation, and sent back to the customer.
I have used the dishwasher method to clean variable caps, ceramic & bakelite coil forms, etc. with good success. Just do not forget to re-lube the capacitor bearings, and shaft bushings, as they can seize or rust up.
If you have mica padders and trimmers, you might want to remove the mica sheets to be safe. Again, don't forget to place a miniscule drop of oil on the adjusting screw. I use a cotton swab with a tiny amount on it, and just gently wipe the threads. If you can see it puddle in the threads, you used way too much.
DO NOT USE WD40 ANYWHERE IN A RADIO!!!
It creeps, and WD= Water Displacement. It's NOT a suitable lubricant. Your radio is not a car.
Never spray it where it will get on rubber belts or drive wheels. (I have worked on more than one car cassette deck or VCR where it was "squeaking", and the owner decided that WD40 or 3 in 1 oil spray would cure that. It is almost impossible to clean up a tape deck or VCR that this has been done to. They are "dumpster meat". BTW- The "squeaking was caused in all cases by defective tapes).