I have had the some problem on both my rear door electric windows. The local dealer said its the motor, but upon further investigation and some advice from an independant dealer it turned out to the metal regulator that slides up and clamps the window in place.
A lot of vw breakers said I had to buy the whole bit including motor, what I found was that you can get a regulator off a manual windowed golf that it's exactly the same part. Ok I had to buy a manual window mechanisim(which will go in the bin) for £7

, but cheaper than trying to but an electric one.
You need some small pliers to get it off and maybe a small flat terminal driver to leaver the old one off, make sure when you remove the old one that electric window is about half way down this makes life much easier especaily when fitting a new one.
This seems to be a common problem, make sure you do this on a dry day or have a garage.
I had thought of getting a batch of new ones made up and selling them on ebay how hard can it be?


Good Luck