The shop looked at the car again today and determined the torque converter is the cause of the vibration (in their opinion). The tech said he could see it wobbling when he looked through the bell-housing grates. He said without removing the transmission he could know for sure and that the fly wheel could also be the problem, but he leaned toward the torque converter. They knew the transmission was still under MBZ warranty so they called the dealer and tried to arrange an appointment for me.

Proceeded to the dealer, explained the situation and problem and set up an appointment for tomorrow morning. The service advisor spoke with his shop foreman who speculated either the balance weight had fallen off or the shaft on the torque converter was bent. The dealer was relunctant, but after $4500 for the transmission and two follow up visits (before going to the indy) for $100/each citing this very problem, there isn't much argument in their favor.

Back at the indy, they replaced the ignition wires which had been ordered earlier, but not installed. I haven't thoroughly road tested the car, but i think that resolved the intermittant (and very minor) mis-fires. To credit the indy shop, despite alot of parts:

For the vibration:
Rebuilt the fuel injectors
Replaced the infamous wiring harness
Replaced fuel filter
Replaced ignition wires

For the cold start problem:
Replaced crankshaft sensor
Replaced air temp sensor

General diagnosis included:
Electrical test & scoping the ignition
Fuel pressure test
Various other guesses & head scratching!

They waived their labor and sold the viscous fan for 1/2 their cost (paid around $200; the fan was part of earlier problem with the engine temp). As mentioned before, everything thus far is reasonable maintenance or preventive maintenance for a car with 96k, so I'm not too upset about the money. But what I appreciate the most - they waived their labor without my asking are worse yet, having to argue.

The indy is Park Place Ltd. in Bellevue, WA and they have a new MBZ tech, Dave, who came from the Phil Smart MBZ in downtown Seattle. Dave, the new tech, also nailed the cold start issue in one shot. I would definately recommend Park Place Ltd - and considering the MBZ of Bellevue charges $115/hour, Park Place is very, very reasonable (around $60/hour).