I used some carpentry clamps to spread my sliding window frame apart
slightly, and after taking the rubber channel out the windows came out
"easily" with no need to remove those two little plastic sliders...and
no fear of breaking anything.  I also found some of that fuzzy weathers
tripping at Home Hardware...likely cheaper than VW.  I used a spot of
silicone to hold the rear most end of the rubber channel from falling
down upon reinstallation because the window holds the rest in place.

BTW, if you have an early Vanagon and are replacing the plastic sliders,
I think only the latter plastic sliders are available.  I used my
Dremmel to modify the aluminium track to accept the new plastic slider
which have a little locking mechanism in them.  I tried modifying the
plastic sliders the first time I did this and they only lasted a little
while before I lost them when the silicone I used to secure them failed.
The replacement ones have now been in place for 3 years because they are
held in there mechanically...just like the latter Vanagon ones.

Pascal
'84 Westy