Submerging with the power on is usually a death sentence for the speed control. Motors, servos, and receivers usually survive a dunking if they're allowed to dry thoroughly before you attempt to use them again.

I have an E-starter myself, and I really don't see where too much water can get in, unless it goes completely under. The problem with sealing everything up is twofold:

a. Getting tape to stick.
b. Cutting off cooling airflow to batteries and motor.