I gotta wonder about the microwavable part, too. What the hell is that about?
Anyway, I'm guessing that the problem is the plastic is fogged up somehow. Certain chemicals will do this. Simple Green is one of them. (Great cleaner, bad for that clear plastic part.)
If it's sort of milky looking, then there's only two ways to go about dealing with it.
A. Replace it
B. go to your local auto supply store and buy some polish specifically designed for clear plastic. If it;s minor, going over it with the polish may do the trick.
if it's very damaged, you may want to wet sand it with 2000 grit paper or so before hitting it up with the plastic polish. I had to do some repairs to the instrument cluster in my truck once when a girlfriend tried to clean up the grime-coated steering wheel with Simple Green. By the time i was done, it looked like new again. I couldn't say that for the steering wheel.
