I need help handling my mechanic

[MikeMcMo]

Hive mind, please help: My '99 base developed a klunky little rattle from the right front quarter when hitting small bumps. There was no decrease in performance but I worried about safety. Seemed like a non Porsche-specific issue so I took it to my old favorite mechanics. For $800 they replaced the right lower front suspension control arm and both front suspension stabilizer bar links. They showed me that the ball joints and connections in those pieces were a little loose. I drove the car away and the noise was still there, exactly as before, performance the same as before (just fine). So I took it back and they were able to determine there is about an eighth of an inch of play in the bushing or the bearing just beneath the strut plate. That will take another $400 to remedy when I'm ready.

They are telling me to come back and they will do whatever it takes to make me happy.

I want to tell them to eat the labor on the first job and the second, and that they should do the second repair for free. Maybe their markup on the parts will help cover them for this. Do I have a leg to stand on with this argument? They apparently made an erroneous diagnosis on the first repair, probably an honest mistake, but an expensive mistake for me. It could be that these parts were *almost* due to be replaced, but I can't be sure. I may be replacing the car soon, and that $800 control arm/stabilizer bar repair would have been an expense for the next owner to bear.

Do you think I can reasonably go to them and ask them to do the $400 repair for free, now that I paid for the unnecessary or premature $800 repair? Thanks!