Ok, so I've been searching for the last 3 hours, and I have found lots on waterproofing esc's, servos and such, but very little on motors. The best I found was here,
http://www.rc-monster.com/forum/show...ght=waterproof, posted by Sedri. Here is a quote from his post on waterproofing motors:
"As for the motor itself, I haven't figured out the best way. Some people just make sure the rear endbell is clean, then cut a square piece of good quality electrical tape (which is rubberized, by the way) and put the square of tape over the rear bearing area. That way, you can EASILY and very cheaply check and replace this "cover", and it's foolproof for a quick romp in the snow. As for where the wires go into/through the motor (if you don't have a Lehner with the brass tubes, that is) RTV sealant, just enough to seal that area, seems to work great. The only problem left is the front endbell/output shaft if you use an endbell mount. I use canclamp mounts, so this is no problem for my motor. Simply another trip to the hardware store, ask where the plastic table-leg/chair-leg end caps are, and look for one that will slide snugly over the end of your motor (typically 36mm for "540" sized motors)
You will only need to drill a hole in the center for the output shaft, and the plastic caps conveniently have a dimple right in the center already, so it's super easy to put a hole in the center. This won't be 100% waterproof - you can't drive it underwater - BUT, in my Landmax Rally, which I've driven in the rain, through puddles, in the snow and generally everywhere, my only contamination problems have been with seizing and/or rusting wheelbearings - and those were rubber-sealed bearings, no less! Water was running off of everything after my most fun drive in the snow; you'd think that I had driven my car through the car wash!
Good luck!"