I have two 2002 Polaris Trail Touring sleds that both have the identical problem.
Moisture (or condensation) has developed inside the headlight lens on the right
side only (from sitting on the machine). I can't see any cracks and can't see how to fix it except removing the headlight bulb and trying to dry it out with a hairdryer.
Any ideas as to why this is happening and a proper fix?

I would put out the entire headlight assembly and fill with water and see where you are getting moisture in. Once you know, seal it with some clear silicon or glue and put it back in.