I know this is late, but I figured I'd add it just in case someone else runs into this thread. I've rebuilt my HBW150, and posted a long description of the process here
. I hope it turns out to help someone else.
By the way, once you get the thing apart, you'll see that the shift-level-movement requirements in the manual are a little misleading: you do have to shift as far as they say, but you can shift farther without any worries about what's going on inside. (Don't shift so far that you can't get back, i.e., so that your cable and the arm are lined up!)