How fast are you going? I remember the second day I got my bike, went about 15mph into a 2-foot deep hole and flooded my case pretty bad.

 

Im one of them, who hasnt had water problems...but ive only gone into water up to the headlights.
Id say there must be some loose clamp, or missing plug on the tubing going to the tranny. Maybe theres a misalinement, with the joints. Theres a drain plug on both the forward and aft tube, and four hose clamps on the tubes. And a drain plug at the bottom of the case.
I know lots of guys with grizzly and kodiaks, and havent heard any wide spread problems with water, getting into the belt area. Usually its known why it got in there, such as drowning it out.
If waters getting in there from just normal riding...then somethings not hooked up right.

 

Never had water in the belt on mine, but I'm leary as hell about it every time I get around water. I hate CVT's regardless of whether I own one or not, and regardless of what brand of quad it is.

 

ill cheack on mine to see if thats the problem