I had a problem with some clear front corners - one of the reflectors
came loose and I had to take the lense off to fix it but the
sealant/adhesive they used made it impossible.
So I put the whole unit in my oven and set it on low.
5 minutes later it was a little hot to the touch, but not bad
and I was able to pry the lens off with a screwdriver.
I fixed the reflector and repeated the process to reassemble.
I figured if it worked on the fronts, it should work on the rears and
would be a lot easier than using a hair dryer.

 

many people including my self have cleared their rears that way.