FYI-
just a note -  the drivers side sliding side windows are the same size from
'80-'91, westy or regular window, and all drivers side windows are
interchangable thru all years for the drivers side.  
in other words, you can put a '80 drivers side slider on a '91 and vise versa.

BUT...   when VW changed the sliding door in '85, they made the slider door
window smaller...by about an inch exactly.  so you can only use the 80-84
passenger side slider door windows on a 80-84, and the 85-'91 passenger side
slider door windows on a '85-'91
why did they do this?

who knows.
anyway, hth
chris