SMC 70-210mm F4 help

[Joaquim Carvalho]

I have two A SMC 70-210mm F4 lenses. The collar on both these lenses 
will slowly slip if the lens is pointing down (not too bad but I love 
these lenses so much I really would like to have them fixed)
I read on Stan's site something written by Bill Peifer on this list that 
suggests that the lenses can be fixed:

Bill Peifer - (...) One thing to watch for on these is looseness in 
the zoom/focus collar. The collar on some lenses will slip, thus 
causing the focal length to change, when the lens is pointing straight 
up or straight down. It's easy enough to fix -- simply roll back the 
rubber sleeve on the collar and tighten the screw. (...)

Which screw does this refer to? (I can see quite a few when I roll back 
the sleeve)