Sorry to resurrect a dead thread, but I have something to add.
Two years ago, I performed a fix similar to the one described and pictured by 98FLSTC. My posts are still up there.
My solution was much more crude, and involved a nail with a fat, rounded head rather than the special "knob" type part he found. Mine worked great for two years, but last weekend it finally crapped out for good. I guess my drilling caused a crack? I dunno, I haven't opened it up yet.
Anyway, I went looking for BMW part #64118398937. The median price I found was $219. The lowest was $192 (but I'm not sure they really had it in stock) and the highest--you guessed it, from a REAL BMW DEALER was $515.
Then I checked ebaY!!!!
$86.27 shipped. They have three other assemblies listed at $150 OBO. It is certainly worth considering.
If someone were really smart, they'd figure out how to make a mold for just those little plastic arm thingys. For less than the price of one assembly you could probably manufacture 100 of them, and sell them for $50 each.