I had same prob with my 320i e36,I had my door panels off loads of times with no joy,paid a windscreen company money to take glass out and put it back in correctly and it worked for about a week then started again,so I ordered the mechanisms from bmw for £60 each and replaced them and now they are as good as new.hope this helps
shaun www.sdwupvcrepair.co.uk, October 2008