I have a simple solution to your problem.It was passed on to me by an old school shooter who saw me plagued with the same delima.I purchased a cheap tele-zoom for my Yashica FX3 and it slid back and forth at will. Heres what you do.
Extend the barrel to its full length.Cut a strip of electrical tape to fit the entire length of the inner barrel and apply. If that doesn"t work repeat with another strip on the opposite side of the inner barrel.You may need 3 or 4 strips.
I have 3 old pieces of glass that have been made workable using this method.

Good Luck,
Mike