[ChrisBennet]

I don't know if this is the same problem you are having but maybe it will apply. From my archives..
-Chris

If you have electric seats that are jammed but the motor still works (or
tries to work), read this. It applies to 928 S4/GT, 911 Carrera 2/4, 944
S2 models. This is one of those jobs that takes 30 minutes to figure out
and 5 minutes to do. I hope that my explanation helps reduce the time.
The seats on my '88 928-S4 have worked perfectly since I applied this
TSB.

Porsche Technical Bulletin #79003 December 1990

928 S4/GT, 911 Carrera 2/4, 944 S2 electric seat jammed in backward stop
position. Electric seat motor not powerful enough to pull seat from
stop.

The stop washers on the seat rail threaded rod are modified (harder
material) from production date June 5, 1990. The color of the new washer
is white (previously light brown). Note: Some of the washers on my '88
928 S4 were black and some were dark reddish brown. The washers are
about 3/4" in diameter and 1/4" thick.

The stop washers are not available as spare parts. If the seat is jammed
in the backward stop position on earlier cars, cut the stop washers with
a side cutter or similar tool (dykes) and discard.

Keep in mind that the rear stop washers are actually on the front part
of the threaded rod, in front of the stationary nut that the threaded
rod acts on. The forward stop washers on the drivers seat were missing
on my car as though somebody tried to install the fix but cut off the
wrong washers.

The method that I used on my '88 928 S4 was to raise both the front and
rear of the seat and put the seat almost all the way forward. I found
that on my car if I hit the forward switch many times with the engine
running (for higher voltage) it would come unstuck and finally move
forward. If your seat wont go forward, don't try to hand crank it with
the "speed wrench,"You will probably only break the plastic gear. Pull
the cables out of the motor and try to free each side individually.
There is a nut at the end of the threaded rod that imbeds itself in the
stop washer and keeps the threaded rod from turning. As a last resort
you may be able to cut the stop washer off with a knife to free the
threaded rod.

It's hard to see under the seat and the stop washers are all the way
forward on their threaded rods and you can't get to the stop washers
from the front of the seat. Looking forward from behind the seat, look
behind (to the rear) of the stationary nut, you can see what the front
stop washer looks like. It is identical to the rear stop washers (which
are at the front). Reach under the seat and follow the threaded rod all
the way to the front with your fingers. The washer will slide back on
the rod with some effort. Pull it back almost to the stationary nut. You
can see it now. Cut it off with your diagonal cutters. It is made of
hard rubber. Do the same with the washer on the other threaded rod. Also
do the other seat.

The TSB also says to move the seat at least five time against the
backward stop position with someone sitting in the seat and if it still
jams, replace the outer seat rail.

Left Seat Outer Rail: Part Number 928 521 489 08 Right Seat Outer Rail:
Part Number 928 521 490 08

It is relatively easy to remove the stop washers yourself so it would
probably be easier to do this job yourself rather than take it to a
Porsche dealer. I don't know if this is a free fix or not, you could try
Porsche. If you remove the washers and still have the problem it would
be worth a try to have the Porsche dealer replace the seat rails.

Earl Gillstrom '88 928 S4 5-Speed