I had a zoom control problem on my GL2 as well. Started as an intermittant thing, but became more regular. I’d begin a zoom and it would not stop until I tapped the control in the other direction. Or it would begin to zoom on its own.
Good news. I had the problem repaired at a shop in San Diego. They’ve been around awhile and another Canon using friend gets his stuff taken care of there. It’s $100 deposit towards repair to check it out. The total repair cost me about $200 including the part. (they replaced the zoom control switch). Nice guys too, been doing pro video repair for something like 20 years. They’d be able to help you figure out if there is a contact issue as was mensioned by someone else.
Con-Pro Video
4646 Convoy St # 113
San Diego, CA 92111
(858) 495-0392