Doug,
I have a '79 300SD. When I first got it, my drivers side regulator snapped in half. Then, two days later the rear window broke too. Two regulators, in a week. over 300.00 dollars. You can bet that I took the other two door panels off and greased all of the sliding surfaces really well.

You can replace just the regulator, the motor is quite separate from that.

As far as bending the toothed jaws back into alignment, I don't think you will have much success. The reason being, that the regulators are pot metal, and are very unforgiving. They bend over 20 years and don't bend back. Eventually they get out of alignment like yours and snap from the stress.

Sorry for the bad news. Take care of the other three.

Replacing it is straight forward. I think if you have the window down to the point where you can see the bolts for the regulator through the openings in the door you will be fine. You can always hold the door panel up to the door and hook the wiring up to adjust the window level.

Grease Everything!!