Step 11: 6) The Ultimate Waterproofing Method
This is the most effective method for waterproof. The first step is to open up your servo.
Now get some waterproof epoxy. Make sure its non-conductive!
Now place a big glob of the epoxy onto the circuit board. Spread the epoxy around real well. This particular epoxy expands slightly when it solidifies.
Now using a syringe, inject mineral oil into the gear casing. This is a little messy . . .
Fill it until its like 90% to the rim (the rest will spill out if you put more in).
Now after you put the O-ring onto the servo, put a little oil on it to reduce friction.
I like to tape the servo down so the epoxy can cure properly overnight.