The verdict is in on my E300: It indeed is the transmission! Apparantly the B3 band fragmented internally, and the shop was amazed it was still driveable. By-the-way, the tranny mount and both motor mounts were also badly worn, and may have contributed to the problem. So, the total cost of the entire job (with a tranny rebuild, torque converter, and all replacement mounts, fluids, recycling, labor, tax, etc) is setting me back $3700. The dealer wanted $6800 for the same job, but it was fresh in the crate from MB, had an extra year on the warranty, and came with a small tube of Vaseline...Thanks for everyone's suggestions and help!