I replaced my seat bushes recently and took some pics, so I thought I'd have a go at a short guide.
There are youtube vids available but they are a bit long winded and seemed to miss key parts.
Its from memory so I expect I've forgotten bits, but hopefully will help someone.
Before you start, make sure you have the following tools;
T50 Torx bit
T25 Torx bit
5/8" Socket (Possibly should be 16mm which I don't have, but I do have 5/8" and it works fine)
preferably 1/2" drive for the sockets. A torque wrench is useful too.
I followed the advice given in other threads, that is;
*Once your car is unlocked put the keys away - don't put key in ignition until complete*
There is a risk of getting the air bag light on otherwise apparently.
With the seat fully back, undo the two 13mm nuts from the front of the runners;
Now put the seat fully forward, and remove two 5/8" bolts from the back of the runners;
Lift the seat off the threaded bolts at the front so it is loose on the floor and then slide the seat as far back as it will go on the runners.
Disconnect the seatbelt from the seat using the 5/8" bolt.
Now carefully tip the seat forward, and either put some blocks under the back to wedge it forward, or turn it towards the centre of the car, remembering that it is still connected to the seat wiring loom;
You might want to cover your door sills at this point to prevent scratches etc.
Now look under the seat and disconnect the wiring loom;
2 connectors on my car, but you might have more if you have heated seats perhaps.
Now lift the seat clear of the car and put it facing downwards where you can work on it.
Now is a great time to clear out and vacuum the space in the car where the seat was. There was almost 3 quid under my drivers chair. This is the job that just keeps on giving.
Pick a side (left/right), and undo 2 T25 torx screws from the runner, and the T50 torx from the threaded bar;
The left and right hand sides look similar but not quite identical. The procedure is the same for each though.
Now measure the position of the runner. There are a few ways of doing this, here's a couple of suggestions;
Now gently pull up the threaded bar, and move the runner with it to help it out.
You should now have something like this;
Measure the position of the inner threaded block on the thread itself to use as a guide when re-assembling.
Now unscrew the lot;
Yes, that mess in the middle is a BMW seat bush...
Replace the bush;
I've used acemans replacement bushes, they need to be sanded down to around half their original thickness to fit, and you need to do them as evenly as possible so the threaded block is in the middle of the cage. P60 sandpaper does the job, careful not to go too far.
Heres one finished next to an old one;
And heres both done;
Screw the cage back on to the thread, to the same position from which you removed it.
Put it all back together - refitting is pretty much the reverse of removal.
I torqued the seatbelt bolt and the rear seat bolts back up to about 50Nm, based on values I got from a 3 series E36 service manual. (haven't got a Z manual yet).