At 91K miles, the interior of my 91 M5 is still in great shape, except for a little wear on the driver's seat. Of course the passenger seat is nearly perfect. I noticed the part numbers are the same, so I switched the seats this weekend and thought you might want to know how it went.

Bottom line: There are minor differences in the plastic panels that house the switches. If you look closely, you can see a line about 1.5 inches high and 6 inches long where the inside panel left a mark on what is now the outside of the seat. Hopefully, this will diminish somewhat with time. The idea is to balance the wear between the front seats, so I am OK with this minor blemish.

Parts you will need
Plastic rivets
Zip ties, 7" black (about 3 dozen!)
8 crimp connectors or soldering iron and shrink tubing
Friction tape

Special tools you will need:
T25 Torx driver
E14 Torx socket (this is like a 6 point socket)
Torque wrench
Panel tool for pulling out plastic rivets (optional - I got mine from Crutchfield)

Pull the seats at per Bentley. This is where you need the Torx socket. I lifted mine out by myself, but it would be best to have two people.

This is a good time to clean the carpet. We have a Hoover carpet shampooer with a stair attachment. Works great.

Remove the side and back panels as per Bentley. This is where you need the panel tool. There is a plastic rivet at the rear and on on the bottom for each side. This is where you need the Torx driver.

Basically, the only thing different between the seats is the wiring harness. The hard part is the connectors in the seat back for the heater and headrest. I could not figure out how to remove the wires from the factory connectors, and the connectors won't feed back through the wire guide at the seat back pivot point. It might be possible to remove this if you took the seat back off, but I doubt it. I decided to clip the wires, unwrap the friction tape and feed them through the tubing that goes to the seat bottom.

Getting the harness out of the seat bottom is pretty straight forward. Remove all connectors, clip the zip ties and pull the wiring harness out through the seat control opening.

Hint: Study the wiring harness carefully. Leave the clipped zip ties in place to remind you where the harness goes.

You will notice the opening for the seat control is already partly cut. Finish cutting the sides and bottom of the opening, but don't go all the way to the upper corner. Stretch the flap you have created down hard and hook the hole on the tang inside the opening.

Feed the harness into the opening. Attach connectors, replace zip ties, feed the cut wires up into the seat back. I prefer solder and shrink tubing. Replace friction tape, connectors, and zip ties.

Hint: If you cut the wires in the seat back, switch the connectors too or the wire lengths might be uneven.

Switch seat belt clips.

Replace side and back panels. The inside panel just barely covers the hole left by the seat control when it was on the other side of the car. It covered the hole on mine, but I did have to play with it a bit.

Hint: Push a bit of soaking wet terry cloth up inside the outboard bolster (above the seat control) to get the leather wet. The leather will shrink, reducing the dents I mentioned above. I failed to do this on the passenger side, and I can tell the difference. Wetting the leather from the outside does not seem to have the same effect.

Reinstall the seat, again, four hands are recommended, but I did it myself. Torque seat belt and seat fasteners to 36 ft-lb (48 Nm).