Tom, I don't know if you use it at all but I've found stiff focus rings usually respond well to white lithium paste.

A good dab to the helical grooves and a lighter smear to seals and rings usually does the trick.

I applied this to a Sekor 80mm  while back and it's behaving itself quite well now.

Just don't overdo it on PushPull style zooms or they'll continually droop when pointed downward.