As opposed to trying and waterproofing the whole servo, why not just waterproof the circuit board, because that is what shorts out and causes poor performance of the servo. Use a good water proof epoxy, on the circuit board, because CA is conductive. Or if you really want to go overboard, you could then use the CA on the joints, and then the tool-dip on it.
Haven't tried this out yet, bet am planning to soon.
I think that Steve Reichmuth uses waterproof servos in his Trenchant. Any tips, Steve?