Very common problem that can be solved with $0.30 worth of washers. It sounds like you need to offset your motor with washers to "bring in" the armature that contacts the nylon bumpers :
You are correct that this is a drivers side only problem. Here is a picture that shows no washer offsets. This is what causes the armature to chew up the tips of the nylon tabs. Compare this to the picture below, and you can see how the tips of the nylon tabs will get eaten alive without the washer offset. There is a GM bulletin regarding this problem, and directs the tchnician to fix with washers.
Notice how the motor's drive shaft is shifted more to the left due to the offset washers, which brings the headlamp rotating arm shaft in more direct contact with the nylon tabs, and more importantly, the metal tabs under the nylon covers.
Finally, for fun, this what my driver headlight was doing when the nylon stoppers where chewed up to the point where the armature went past the stops :