600SEL clatters on test drive

I am in the decision phase, whether I should buy a 600 Bj 1992 with 136,000 km (allegedly verifiably true mileage). The problem is that when driving the test drive at the rear left a little bit, if you drive over bumps or on bad road. I then put the car on stage and looked for the shock absorbers or other parts. But it doesn’t seem to be broken. Does anyone have any idea what that could be? After all, the car v get new TÜV/AU on 8 weeks and otherwise also makes a well-kept impression. I’m not sure if I should buy an expensive problem with my W124 260E or rather make it quick again…