Mike, sorry for the delayed response. Right after I read your post I ordered a MAS unit (car is 91 300E 95K miles) and upon further search on this great forum I learned the crank position sensor or reference sensor can also be a culprit. Before ordering one I decided to see if I can replace it on my own and realized that I will have heck of a time replacing one end of cable. One plug is on the EZL unit and the other one is under the oil filter assembly (almost impossible, at least for me) to remove the screw. I am waiting for the MAS unit to arrive after which I will take it to the dealer (Loeber motors in Chicago $260) and have him replace the sensor. Hopefully this will solve the problem.

I had believed only Mercedes had this sensor problem malfunction. But I read in my local paper yesterday that Nissan is recalling their Sentras and Altima due to failure of this same type of sensor (article below).

“Nissan North America is recalling about 200,000 2003 models of Altima and Sentra sedans that came with a 2.5-liter engine because a sensor could overheat in stop-and-go traffic and make the engine die.
The Nashville-based automaker doesn't know exactly how many cars might be affected, nor has it given an estimate on the cost. But the company notified the National Highway Traffic Safety Administration two weeks ago that it would recall 186,279 Altimas and 14,587 Sentras that came equipped with a 2.5-liter engine to fix the problem.
Nissan discovered the problem while doing follow-up work on an earlier recall involving about 630,000 Nissan and Infiniti cars. That recall, which wrapped up last year, was blamed on a bad connection in the electronic control module, a central computer unit that governs much of a vehicle's operation. The cars either wouldn't start, had reduced power or stalled while running.
The fix could involve replacing the sensor or reprogramming the electronic control module.
The problem is not extensive, Pearson said. "As long as there's adequate air flow in the engine compartment, things are OK," Pearson said. "But it mainly happens in hot weather, stop-and-go traffic, the engine compartment heats up to the point where the circuit is broken in that sensor." •

Having the engine shut off right in middle of traffic is the most horrifying experience one can get and the car, being a Mercedes, will not get any sympathy. I am lucky the shut down did not occur on a highway on a middle lane but occurred near my home. I will keep everyone informed if replacing the MAS unit and crank position sensor solved the problem.