I bought a used WR 450 that had a VAPOR installation. The water temp sensor is a plastic fitting that is spliced into one of the water hoses. I noticed a small drip and investigated and found the fitting was broken at both ends such that the hose clamp had nothing to clamp on. I rEmoved all the bits and pieces and installed new hoses all around.
This is the second failure I have seen in three weeks. My riding buddy at the Desert Dash had same issue but dumped all the water out on the trail - not good. Fortunately he has all the parts necessary to by-pass the fitting and we were able to ride back (good reason to carry lots of water). (His is the most complete tool kit I've seen on the trail)
SO IF YOU HAVE A VAPOR CHECK YOUR WATER TEMP FITTING - YOU NEED TO COMPLETELY REMOVE IT TO BE SURE IT IS OK. MY BUDDIES' WAS "EATEN" AWAY BELOW THE HOSE CLAMP