It's easy to replace the parts and they're interchangeable (you just have to flip the tuner peg).
It doesn't matter as they are interchangeable. You just take it apart and flip the tuner peg around (only 3 parts, well 4 if you count the screw). You could probably just replace the part that broke and use the original plate.
Hey! I've got an idea! You should just buy any ol' Schaller BM and just replace the key!!!It doesn't matter. The whole thing is interchangeable b/c the tuning peg can be flipped around to the other side. Just buy one.