I have manged to fix mine, not a job I would recommend unless you are familiar with stripping the seat down to its bare frame, as the gearbox drive cog's retaining 17mm nut is located within the steel box section of the frames sliding seat runner section and, is from my experience impossible acess without a full strip down, and judging from the marks on my seat frame and bolts Im pretty sure I'm not the first to have attempted to fix this seat.....So to the fix I was able to buy a second hand motor/gearbox assembly for the rear tilt motor from Ebay, which appears to be the same as the E46 one, but do check for yourself, certainly looks the same from images I've looked at. As I was unable to access the drive cog retaining nut, I managed to separate the gearbox assembly in situ by undoing the 3 x13mm retaining nuts for the entire assembly (you can probably get away with just removing the two closest to the motor as the third holds the drive cog plate and can stay in place) then undoing the 2 x 10mm nuts on the frame side of the motor, then undid the 17mm nut on the opposite/motor side of the drive cog. Once all undone takes a bit of manipulating, but it will separate from the backing plate leaving the drive cog still attached to the seat along with the outer backing plate. Once off and on the bench you have a large 2 section drive cog along with a smaller drive cog which is driven by the first gearbox All these cogs are steel and should be ok. Remove the main large drive cogs, they just lift out to reveal a small Torx bolt which needs to be removed. Then turn the assembly over and remove the 2 x torx bolts on the opposite side of the housing and this will allow you to separate the first and second drive gearboxes. So the fault I found was at the bottom of the final drive cogs under the steel cog in the first drive gearbox is a large black nylon cog approximately an inch wide which had stripped 4 or 5 teeth allowing the motor to turn freely but not engage any drive to the gears. To repair I stripped the replacement gearbox to the same point as the damaged one I had removed and reattached it along with the motor to the backing plate and drive cog I had left in sutu on the seat frame. Reattaching can be a little fiddly I found it easier to remove the motor with the 2 x Torx bots to allow more room to maneuver the gearbox assembly into place. Pushing down on the seat rear runner also helped with this process. Next job was to reattach the nuts As my seat was stuck in the down postion the height adjustment frame made one of the nuts as was the case with removing it difficult to access, so I tightened the one that could be reached then plugged up the seat next to the car raised the seat rear height adjustment which moved the frame past the nut allowing me to reattach it to the frame side of the gearbox. Hope this helps someone else who may find themselves in this position. Its not an impossible job and I'm sure someone out there will know an easier way, but it worked for me and was way easier than stripping the seat back to a bare frame to access the annoying 17mm drive cog retaining nut.
