What type of silicone to use?
 

What type om silicone are safe to use direktly on the circutboard in a esc?

The Acid in most silicone sealants corrodes copper and destroys PCBs, you have to use electronic grade acid free silicone sealant not the stuff you use for your bathroom or fishtank, this is the stuff I use to waterproof the RXs and ESCs I use in my boats.