Couldn't tell much from North Hollywood web site, and wasn't ready to waste their time with a phone call at this point so i did a little web searching. Given the menu of common repairs on the link below i think i may not be the first to notice this....
http://www.dnaspeedometers.com/mbz.htm
Next long drive we take, i'll kick on the AC once the dimming starts--that may tell us that shielding from the heat duct might cure enough to make it a tolerable issue. Otherwise--i'm down for a week to send out for repair.