I can't say I've had the same problem with mine. But from what you are describing it sounds like it's unbalanced. Where the tension is higher in one side than the other. If that's the case it could be the cable stretched, an end has slipped, or a bracket is loose. I would get a couple of friends, one on each side to try and side the roof while you work the manual opener. If it opens that way then it has to be out of balance. It looks like repairing it is what you can figure out as the schematic on realoem.com doesn't show simple replacement parts.
Hope that helps.
