A different problem with heater flap motor

After having problem with only getting cold air on the drivers side I've read countless threads on cleaning heater flap motors. Unfortunately it's not that simple, every motor appears to function fine on my car.

In my case the arm had snapped on the motor with the yellow arm on the drivers side. Hoping for a quick fix I removed the motor, grabbed the superglue and went to refit everything. The arm was re-attached and functioned to each of the limits when plugged back in, without the arm attached and the temperature changed. At this point I was feeling quite chuffed that I'd avoided having to find/buy a new one...

Trying to screw the flap motor back into the car in was obvious that the lever the motor pulls on didn't move enough to reach the motor in it's extreme position. I fitted the motor in it's mid position, it worked for a bit but when the motor wound itself to the end of it's travel it just snapped the arm again.

Obviously a glued together part isn't as strong as a new solid part so I will find a replacement but I suspect the other end of the mechanism isn't moving as it should. Has anybody else had problems with the arm snapping? Could I have some foriegn object blocking the flap this motor moves? and if so any suggestions on how to get to it?

(Why couldn't have been one of the ones on the passenger side that are easier to get to?!!!)