Sounds like it might be the part of the mechanism that keeps it from changing speeds while the motor is switched on (44), maybe the pin doesn't move out of the way? The best thing I can think of is look the underside while you try to operate the speed lever, you should be able to see what's hanging it up. Whatever you do, don't force anything :-o
And wash your hands after you touch those levers ( you've probably heard that before ).
And wash your hands after you touch those levers ( you've probably heard that before ).