a couple of suggestions that you may want to try before driveline work... if you still think it is tire related, try rotating the tire /wheel assemblies from front to back, and also make sure that the lug nuts are hand torqued to spec.(I've owned other vehicles where the torque value is critical to proper rotating balance) I'm not sure what balance machine your tech has, but other threads here indicate that there is a balancer out now that is extremely accurate, you may want to find where one is and give it a try. The dealership that i frequent has a machine that will apparently identify such things as a thrown interior belt. (maybe he is bs'ing me, not sure)
good luck, let us know how you make out.

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Mithra

93 sl600
93 600sel

A mercedes is an inanimate object and therefore must respond to logic and reason.