I've been flat towing my 1997 M3 with 200,000+ miles on the ODO behind our motorhome since Dec 25, 2016. That is more than 19,000 flat tow miles and about 8,000 fun side trip miles. It started pulling to the left on accel even after putting new tires on it. I emailed the local BMW CCA president and as it turns out he is an owner of SinCity BMW Service Center in Las Vegas. They had an opening for a free inspection and as I suspected the RTABs were shot. The installed new OEM bushings with poly side washers for reinforcement the next day. All is well for a reasonable price. Even reasonable for a guy that usually does his own work. If you happen to be shopping for a used car in this area, they also do buyer inspections. To quote Chris; "We tell everyone a Pre-Purchase Inspection, is way more fun than a Post-Purchase Inspection. We charge one hour, and if they buy the car, they can use the hour towards any repair recommended in the inspection - because unlike most Dealers, we wouldn't charge you to tell you how much we are going to charge you..."
