Stripping the sunroof is a relatively easy but time consuming task. On the D2 you can remove the sunroof assembly completely without removing the headlining but it is a bit fiddly. If you strip one side of the mechanism at a time (after removing the glass) then you can use the un-assembled bit for reference when you have got some spare bits left over - ask me how I know :oops:
Whilst the mechanism is out, it can be operated with a suitable torx bit to ensure that it opens and closes easily. Pics here
http://rides.webshots.com/album/560965843pskmVW?vhost=ridesI just need to do the front one now.
One question, Why do you need a (or two) sunroof in a vehicle with climate control???