Jack,
That King HF radio was a bargain at $30. Hope you can restore full transmit power.
HealthKit had similar reliability problems in their marine radios. They failed far too frequently. Most failures were corrosion related. Arcing. Bad contacts. Etc.
MFP varnish seen on military radios mostly solves the problem but no commercial radios I saw used it.
We put some kind of petro vapor emitter strips in marine electronic gear. It helped but didn’t totally solve the corrosion problem. We sprayed silicone oil on the rotary switches. Didn’t degrade their functionality and kept them free of corrosion.
What worked really well to keep connectors working at sea was to slather pins threads and sockets with silicone grease. Dow Corning silicone stopcock grease worked just as well as the more expensive dielectric grease. The metal to metal pin and socket connections still worked fine. I think the tight interference fit displaced the grease.
My father, who was a fishing boat captain, wasn’t very romantic about the ocean. He told me “it wants to sink us, drown us and wreck all our electronics.”
Mark
AF6IM