No you can't take apart the esc without voiding the warranty on a Traxxas vehicle. If you do run in water just be sure to follow the instructions in manual and be sure to oil all the screws so they don't rust. I've put my e maxx through pretty much everything; snow, mud, puddles, rain, rinsing it off with a hose, jumping off the end of a dock. I've never had any problems with it. Just be sure to care for it properly and give it lots of love and it will last forever.
Hope this helps