Unless it's been in the last couple of years, then I have to disagree. Motors with the "AF" suffix on the engineering number sticker are the last update I'm aware of, and involved making the actuator arm fit tighter on the output shaft. Contrary to popular myth, the arm is not "permanently" attached to the motor on those later actuators. It can still be pried off, it's just a press fit, and it will still crack. The last time I replaced my arm, the broken motor had the "AF" (latest) number. If there's been an update since then. I'd like to know.
Part of the issue is that the geometry between the two arms (black and gray arms) is off. In the full heat position, the gray arm hits its stop about 1/4" before the black arm does. This causes stress and will either split the black arm (usually) or the end of the gray arms snaps off (more rare). The solution is to make one of the holes in the link between the two arms into a slot.
What I'm looking at now is based on a thread posted in the markviii.org site, where a guy had pics of the actuator going way past its own stops. I want to test it for myself.
Humor me. ;-)