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Thanks, that makes a lot more sense. Any advice on disassembly? It looks like there are seven small Philipshead screws holding the back on the camera (three screws on the bottom and four underneath the eye cup). Would it just be a matter of removing those screws and lifting off the back to get access to the internal parts of the quick control dial?
John, I believe you'll find a couple of more screws underneath the grip rubber. Peel it off carefully, leave it sticky side up, and it will usually stick back down just fine.
When you have the rear plate off there are two large flex cables attaching the back to the main PCB. Undo the latches, slip the flex out, and then you can turn the back upside down and you'll see the inside of the quick control dial.
I've found spraying a little contact cleaner like Deoxit on the inside of the dial and rolling it around a few times usually takes care of it. I wouldn't try disassembling the dial unless you're really handy - there's a lot of little parts inside there.
If you're really careful (especially if you have another pair of hands to help) you might be able to get some cleaner onto the dial without disconnecting the flex. The only danger is in damaging the flex cables / connectors. If you do, it's off to Canon for a main PCB replacement.