Boy, real nightmare now.....
Um, my feeling on the timing issue, in general I feel that if it is "capable" of running OK, but later on during a test drive it starts acting up, doesn't really make me feel that they actually harmed anything by replacing the sensor. As long as they were careful to not move the TDC sensor barcket AT ALL, the timing should be close enough. It's not the kind of thing you mess with, takes a dial indicator down the #1 plug hole to get this basic timing set correctly, real precise work.
Only 1 O2 sensor on this car, they added the second sensor way later, mid 90's.

I hate to berate a mechanic, it just doesn't sound like they know their way around a MB, and then using all the wrong terms, such as referring to the TDC sensor as a crank angle sensor (a crank angle sensor keeps track of the entire rotation, the TDC sensor is rather archaeic (sp?) and only senses when #1 cylinder is at TDC (top dead center). The newer engines use a crank angle sensor.
And also referring to a second O2 sensor......
Also the problem doesn't seem like a bad O2 sensor would cause this problem to me.
Probably the best starting place is to get some testing equipment set up on it and then get it in the failed state. What would come to mind first would be a fuel pressure gauge (the kind where the gauge dial can be observed while driving, usually it rests on the outside of the windshield), and various voltage or amperage readings can also be monitored, such as the EHA amperage, the fuel pump amperage, or the engine control module supply voltage. Not all at once of course, but this is a better approach than just driving it, having it fail, and then just saying "Huh, that didn't fix it, what should I replace next?"

Gilly