Grease yes I added a lot on shaftEven in a car, the ECU inside the cabin is almost hermetically sealed. And here are electronics that are outside at a height of tens of centimeters from the ground (puddles, sand, dust, dirt)...
All you had to do was at least lubricate the gasket with thick grease, if you don't have silicone sealant. Maybe you have additional bearings also? Are they sealed?
Leak could be thro' the casing joints or the cable entry my first guess. But just slowly check all around.