Allen, yes, the weight of the particular elements will always seem to be affected by gravity, no matter what the make is, except for the autofocus variations held in place... But when new, some lenses had mor grab to the movement. What usually enhances the sliding in thirty years? Some sources say the helicoids, some say the grease goes. I don't plan to take these things apart any time soon, but thought someone out there might have a more hardware- oriented solution that should have been addressed bythe manufacturer.