The door handles are intended to be one-time-use. A small but significant design mistake on BMW's part, as it would have been easy to design them to be service removable and re-installable.

The upper end of the door handle does indeed bolt to a steel flange that is welded to the door itself, but the handle also needs to be attached to the door panel, for added pull strength and to help with installation alignment on the leather panels. A 1/2" long pin is formed as part of the vinyl core of the handle and protrudes outward, inserting through a hole in the door panel. You then melt the pin over, mushrooming it out over the back of the door panel. Removing the door handle means sheering off this mushroom, which renders the pin useless for re-installation. Which means... you have to buy a new handle.

New vinyl handles (Z3) are around $65 each. As I recall, new leather handles (MZ3) are something like $230 each. I've wanted to upgrade to the leather handles, but had trouble getting past the notion that if I ever needed to remove the handle for some kind of leather work, or.. these vinyl pins have apparently been known to break off after a while, ... that this would mean having to replace the handle, yet again.

What I've discovered is that you can re-use the handle by sheering off the pin's mushroom head, dremmel it flush to the door panel, remove the handle, now take off another 2mm of vinyl. Now drill out the flat headed pin. When it comes time to reinstall the handle, take a 1" long body panel screw (medium coarse thread, and a medium sized integrated washer head) and heat it with a propane torch. Gently screw it into the pin hole. The heat will form the pin around the coarse threads (this grade of vinyl is designed to be heated and formed... remember the mushroom head?). Snug it down, but don't tighten it. Wait for it to cool. Now tighten it down with "reasonable" torque (not enough to strip the threads.

When I was drilling the pin out, I also realized that after 1.2" the inside of the handle is hollowed out. A cavity. This means, that if the pins newly formed threads were ever to strip out, it would be possible to do one of two things: Dremmel tool out an opening in the switch bay of the handle, and get a nut in there and switch to using a bolt. Or, drill the pin out completely to a 1/4" opening, and use a "spring out" mini molly bolt.

Vinyl handles are cheap enough to just replace them. But if you're doing door panel work and you want to reuse them, it's doable. Leather handles are expensive enough, that there's even more motivation to reuse them (provided the leather has been kept in good condition, of course).

Not many are doing this kind of work, but I thought I'd pass it along, as it may save someone a few hundred bucks.