JR Xs3 Not for Boat use!! no warranty!!!
I haven't tried it in an ESC but I suppose that it would work. I had an Astro-flite ESC in my boats and it came waterproofed. It works great in servos. Remove the 4 screws and bottom cover, squirt in a few drops, close it back up and you're set.
On recievers, take the case apart then put the servo connectors and crystal back in before using the spray.