Well, here are the pics of my fix. My fan, like probably most of yours, sits just barely off the radiator core with just the tiniest bit of space. I was going to shave off just a little bit of the shroud all the way around before putting the rubber on, but decided to give it a try since the material is actually pretty thin, and the legs of the housing are flexible and would compensate for a slightly tight fit.
It turned out to be a perfect fit, and only required a slight compression to snug the housing flange tight under the bolt that holds it to the radiator. This should keep the hard nylon edge of the fan shroud from vibrating against the core now and eating a hole into one of the tubes. I will check it in a thousand miles or so and see how it's holding up and if it's doing it's job with no ill side effects.
The material I used is what KTM puts between the plastic dash piece and the fairing on the 640 Adventure... I just happened to have a extra piece left over that I kept after replacing mine, and I'm glad I did. It appears to be made of a soft PVC material, almost like rubber (could be?). The KTM part number for it is 58214070150
For whatever reason, the listed price for the approximately 24 inch piece of protector in KTM's USA database is about $115, but that is a known glitch in the system... as I recall I paid less than 10 bucks to order it from the local dealer. You'll have to have your dealer call Ohio to work out the actual price... good luck. Note that European and Australian KTM parts sources list it correctly for the equivelent of just a few bucks.
You may be able to find it somewhere else, but the stuff that I've seen in auto parts stores is made of a much thicker and quite hard plastic that wouldn't be suitable... like for car door edges.