Open your windows
does the air only come out of the windscreen vents when selected? it could be that the air's not being channeled properly
Demisters are pretty good in a MKII if it's all in order. I only ever found the rear 1/4 windows stubborn to demist. Rear heated screen sounds goosed although it may well not even be hooked up as that's not your original boot.Often the problem with MKII's is the flaps in the box (ooh er) lose all their foam and become a bit useless. I find taking them apart and slapping on extra panels made from icecream boxes and attached with sikaflex does the job.Nick