I've read where the focus wheel is really only good for the 50.
That the teles are too heavy. I can't remember exactly where I read this atm, one of the myriad of sites where users are sharing their experiences.

My J12 (older chrome version) does similar to what you're seeing but behaves differently on different bodies so Dave's advice about stiff lube on the inner helical/wheel gears sounds like it could be the solution.

I've seen a tutorial somewhere on how to clean/lube the focussing.
Start googleing and I bet you come up with something.

You could also ask over at the FSU forum on rangefinder site.
http://www.rangefinderforum.com/foru...php?forumid=34

There's a Contax subforum there you might try also.