Well so far I've managed to destroy about $1000 worth of ESCs - Seaking 120, CC Hydra XL 240, even a Monster Mambo I semi-potted in polyester resin.....

The question remains: Why don't the manufacturers make them WATER PROOF?
Not "water RESISTANT", not "SPRAY proof" etc. but actually IMPERVIOUS to water.

These devices are sold to consumers in the full knowledge they are to be installed in a marine environment.
I think it's fair to say a relative humidity "slightly above 85%" is to be "expected".

I'm sure a little bit of clever engineering could see an ESC produced complete with internal water cooling plumbing
near the hot bits (think solderable copper tubing guys - excellent heat transferance), and everything encapsulated in
a suitable non-conductive WATER PROOF polymer.

I have used two-pack epoxy resins in the past to "pot" PCBs with great success.

Should we really have to "hit-and-miss" with various cans of liquid goop?
Who-ever comes up with one gets my next $500.