I've done my fair share of Mercedes alignments and I can see that there is some adjustment left in that cam, however, I can't tell you by looking at it weather it will be enough to get into specs, you also have to consider caster. Did your mechanic raise your car on an alignment rack with the suspension loaded? The bushings may appear ok and not falling apart but you may need the weight on them to tell if they are sagging too much. The oil on that bushing in the picture can also damage and soften the bushing. Sounds like you need to find a better place for an alignment then Firestone. I have fixed some pretty bad screw-ups from places like Firestone and Sears. The alignment guy there obviously didn't know what he was doing, most alignment machines tell how to make adjustments often times with pictures if you can't figure it out.