I successfully diagnosed a tire wear situation caused by a steering linkage issue & (although non-500E) am passing on the results which may save time & hassle for anyone running into a similar situation.
Problem: Right front outer tire wear only (Accelerated scalloping of outer edge).
Cause: Loose/worn idler arm bushing (frame end connection)
A friend brought a 1998 BMW 740il series in yesterday to find out why only the outer edge (approx 1.5 inches) of the right front tire was scalloping. His distress was heightened because all tires are relatively new; the car had a recent alignment & a follow-up alignment (which made no real corrective difference). Also, having rotated right side tires, two tires were now affected by the progressive scalloping.
The car is in overall quite good shape, having relatively new steering control components such as tie rods, control arms, etc (factory stickers are still present on many components) and wheel bearings.
Safely placing the front end up on jackstands, I tested for wheel horizontal & vertical loose play. There was audible horizontal loose play. I then went underneath the car to trace the culprit along the steering linkage while my assistant horizontally rocked the wheel back & forth.
I easily discovered the problem was being caused by the idler arm connection on its frame-side end. Loose or worn idler arm bushings will cause front end shimmying. I was extremely happy that the problem wasn’t related to a more PITA component and location. The owner is capable of doing the repair & afterwards can still get a complimentary warranty realignment.
Be aware that the attentive alignment tech should have inspected & discovered this problem beforehand (having had two opportunities to do so). That dealership missed out on a service opportunity & now will be doing a second gratis realignment after component r&r.