Ok - after having replaced the crankshaft position sensor a few weeks ago, there's no more sign of trouble. I'll probably report back in a few months.

One thing I wanted to mention for those of you wanting to try this...apparently there are two designs for the CPS for the 2001 model year (not sure about the other model years). A Mercedes part dealer is supposed to get the correct CPS by looking up your VIN, but this is not always correct; our friendly neighborhood discount OEM MB parts dealer said this is the 4th CPS that turned out to be the wrong one. The best thing to do before purchasing the CPS is to pull the plug out first and inspect it; you can search this forum for step-by-step instructions. The plug will either have a single catch on the straight part of the cylinder, or two catches, one on each curved end; make sure you get the correct corresponding CPS or you'll have to do the whole thing all over again (like me). Sorry, I didn't write the new part number down so I don't know which is which - maybe someone else who had this problem can post here and fill us in.