So, I have a Lumix 14-140mm lens which I love as a do-everything, walk-around lens. Unfortunately the rubber grip on the zoom ring was slipping -- I read some forum suggestions here and there -- one suggestion was to soak the grip in gasoline over night (yeah, right).
I contacted Panasonic service about this and was told it would cost $75. just for them to LOOK at the lens. PLUS whatever the repair charge would be. THANKS but NO THANKS.
So I just slid the grip off and noticed that there seemed to be an accumulation of oils, gunk etc. on the zoom ring and the underside of the grip. I just cleaned both off with alcohol and slipped the grip back on. PROBLEM SOLVED.