I bought this nifty puller months back. It has the left hand thread to secure it self into the threads for the tachometer drive slot and then presses the rotor off the crankshaft.
The old armature was well worn and scored up, but I've been advised that these are German built and almost never fail (don't know why the BMW bosch ones suck so bad then...), but also to buy another if you find one to keep as a spare because these are pretty rare. The problem is, I was supposed to be measuring 1.5 ohms on the slip rings and I didn't measure that on the old one or the replacement. The new one is in much better condition so I'm hoping that I just received the wrong info. The part is guaranteed if it doesn't work, but I just really want to fix this problem.
Now the old BMW one has company on my bookshelf. Maybe I should start a collection of scrap rotors. They do make excellent paperweights