This article is from the VW Technical FAQ, by with numerous contributions by Jan Vandenbrande others.
A: Excerpts from the group:
My 87 GTI 16V needed replacement 3 times. The first two were under
warranty, the third time I decided on the DIY route.
I checked the re-uphostery option, but was too much of an unknown
result.
I decided to buy the dealer part and do it myself. Took the seat out
and removed the old bolster. As it turned out, there was a sharp
weld bead right under where the rip always started!
A few wraps of ye ole duct tape fixed that. I then re-installed the
new bolster cover over the old foam bolster itself. This was a pain
in the ass, because there are these sharp upholsterer's clips you
have to re-bend into place (there may be a tool to ease this, but I
used pliers). The whole thing took a couple of hours.
Anyway, it held up after that. I'm convinced it was that sharp weld
in the seat frame that caused it, and if you have a grinder you may
want to grid it down to smooth it for extra insurance.
Ok, here's two different versions of fixit solutions: #1 find a GTI with
the same seats and get the passenger's seat $35 around my parts for a GOOD
one with NO TEARS or Wear. Then disassemble it and re-cover your driver's
seat with its parts. it's a little more complicated than just taking one
out and swapping the other in as things like the seat belt and slider rails
aren't exactly the same. (they are Really close, but not the same when you
consider things like the seat belt mount point...)
#2 Take the entire seat apart and recover it in a BETTER material. I've
been running my butt across a material called Sunbrella (designed for use
as boat cushion/boat top material). At first, it didn't seem as comfy as
the original, but then again the other original wore out and has since
been covered to match. Mine are done in black which ought to absorb as
much of the scorching South Florida sun as anything, yet they are never
hot like vinyl even when I have the glass sunroof removed at noon. I would
hate to think what an upholstery shop would have charged to do the work my
mom did re-covering my 2 fromt seats because this fabric is VERY un forgiving
when you start stretching it over the frame. There were a few stitches that
mom had to dismantle and re-sew to get to fit just right, but everyone who
looks into my interior comments on my seats. (the rear seat is still done
in the original fabric which is now starting to show its age 12+ years)
 
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