I got around to doing the neat little mod described in this samba thread

http://www.thesamba.com/vw/forum/viewtopic.php?t=381226&highlight=uhmw

I can report that it does work, makes the sliding door quiter. Now how long it will last is another subject.

My blog post about it is here:

http://shufti.wordpress.com/2012/08/23/vanagon-sliding-door-quietening-hack/

It was done on the improved post-'85 style doors, but I would guess it would worth trying on the older, noisier doors.

alistair