Plastic seat fixing - Duravit Starck 3 Wall Mounted Toilet with Carrier

Most seats set with a simple plastic bolt and nut under neath

if you are talking about the plastic piece,its cheaper to buy the whole thing,otherwise,it clips to your seat bar,see pic,

CENTRIC SAFE HAVEN FRONT CHILDS BIKE SEAT

The Key Entry should be a plastic piece underneath the seat, sometimes difficult to find, usually white. You use the same key as the ignition, and turn a 1/4 turn and it will unlock, allowing you to lift the seat off. If it's broken off, you should be able to pull the cable.
Or you can carefully lift the seat up a hair and use a screwdriver to locate the plastic clasp, although this method will most likely break the locking clasp leaving you without a means to secure the seat.

FYI, Most bike shops can locate the clip within a few minutes and are happy to help a new customer, easy fix for them.

I have on a couple of occasions been able to apply some intelligent force and separate the two halves of the rigid black plastic cover of the latch (luckily the bond was weaker than the plastic) and then manipulate the exposed mechanism with a wire or screwdriver or whatever using a strong light and a mirror.

Both times I was able to fit the plastic covers back together after removing the guilty detritus (toffee papers) from inside.

just fixed mine - passenger side. I had to take the seat out, only (2) bolts in the back and (1) wiring connection. the handle has a hole that fits on a pin then connects to the plastic clip. very simple, I would bet nothing is broken just I could not do it with the seat in the car. once the seat was out about 30 seconds it was back on.
hope this helps

Very common problem. The white plastic gear in the tilt mechanism gets old and brittle and breaks.
BMW will want to sell you a whole gear box with motor. Aside from the outrageous cost, removing that gearbox is a pain.
Odometergears.com will sell you just the plastic gear for $40, and their website has wonderful instructions that show you how to replace it quickly and easily.
You will have to remove the seat from the car. Put some old socks over the tips of the seat rails that unbolt from the floor because the seat is rather heavy and awkward to handle, and the tips of those seat rails are very sharp and will cut up the interior and exterior of your car if they touch anything as you wrestle with the seat DAMHIK.
The other tip is to be careful not to over-tighten the screws that hold the cover on the gear box, They are not very strong and will twist in two easily. Again.. Don't ask...
Unrelated, but if the leather on your driver seat is shot, you can use the leather from a junk yard passenger seat to freshen up your driver seat. The seat bottom is replaced foam and all. Don't bother trying to save the plastic snaps, just pry the seat bottom up and put in new snaps. The leather on the seat back has to be removed from the seat and transferred, but it is not difficult.

Metal peg fixing goes "into" large plastic "cup" washer. Metal fixing now goes through holes in toilet pan sitting in the "cup" washer. From the bottom push up the thin round plastic washer, convex side towards the hole. Next the oval shaped thick washer flat side towards the hole. This has a cup shape into which the final plastic screw fitting pushes into (like a coax plug on the TV aerial). This will push up the thread into the cup where the sides force the thread to grip. Finger tighten so that you can still move the metal fixings from the top. Line up the toilet seat holes and push fit onto the pegs. It may take a smart thump to get them fully seated. Before tightening with the supplied black plastic spanner" make sure the large "cup" washer on top has not got trapped under the metal fixing. If all is ok line up the seat and tighten.

There should be plug for the heated seat most likley under it or on the drivers side of passenger seat. This should fix your problem, if it doesn't that means the short is in the dial in the dash. There should be a seperate fuse for each seat in the fuse box. If unplugging the seat doesn't help come back and i will figure out which fuse is the right one and where your fuse box is.

1)move the plastic cover over the seat belt out of the way to gain access to the two mounting bolts for the seat belt mechanism. Use a 10mm wrench and a 14mm wrench and remove the two bolts holding the seat belt mechanism to the body. Use a small drill bit or small screwdriver and make one hole in the plastic cover on each side of the seat belt mechanism (the covers say "do not remove plastic cover". Spray lots of wd40 in each hole. Then exercise the seat belt. When the mechanism allows the belt to be retracted, retract the belt all the way out and exercise the seat belt. Reinstall mechanism with both mounting screws in original position and put plastic cover back in place. Good luck. New seat belt costs $100.00 from dealer and are hard to find working in junk yards. I have fixed several of them this way.

A little plastic bumper, located on a metal tab on the inside of the bottom seat cushions breaks off. It is supposed to hit the seat back release and allow the back to fold down when you push the bottom cusion in all the way. I finally just bent the metal tab up so it would hit the release and that fixed it. (Look for the broken palstic pieces under the seat cusion area as an indication) The dealer replaced the plastic part several times... a waste of time.