[aladin_sane]

I had the exact same problem with a 6139-6002 I recenlty had overhauled. The spring was totally gone. My watchmaker put the watch back together, and there don't seem to be any problems caused by the lack of the spring.

 

[aladin_sane]

My overhaul included new pusher gaskets. Maybe that is helping keep the movement ring in place and the movement centered in the case. I don't have any evidence of the rotor hitting the caseback.