Oh... my SC was leaking slightly and I wanted a new seal. The Honda thing was my cheapest alternative, but only the OD dimension was correct, so I modified one of the Honda Piston and used it.
There may have been a problem with the BMW piston spring end... using it without a spring, but I can't remember now. Probably not an issue.
I did take a video of the clutch and you can clearly see the throw-out bearing backing away from the PP fingers as it's released. I was never confident before that it did that.
