The belt on the Mule's transmission has filtered air supplied to it just the same as the air going to the engine intake. There is a snorkel vent at the top of the Mule's rollcage where air enters the tube and goes down one side to the engine and the other side to the transmission. The filter element is in a sealed case at the bottom of the rollcage that is held in place with six bolts and wingnuts. As an operator, you will need a scuba tank before the engine or transmission get wet or dirty. This is not true of all UTVs, but Kawasaki has this problem licked.
There is a 3010 Mule at Dallas-Ft Worth airport used daily to pick up trash. About a year ago, I asked the fellow operating it how many hours were on the clock. It was over 3,500 hours. I think that speaks very well for the longevity of a belt-drive variable speed transmission. The perceived reliability issues don't exist.