06 K 0020,
I had similar problems with my 300e. Just a few suggestions you
may want to try. Typically, I've found that it could be either
electrical or something in the fuel and/or fuel delivery system.
It could be something as simple as your gas. If you using too
low an octane or if you have water in your fuel. If you are
using a premium octane fuel, then it could be that you may
have a bit of water in your fuel system. This is easily remedied
with a bit of Isopropyl alcohol - the 99.9% pure Anhydrous
works best. Add approximately 200ml, but only to a full tank.
It could also be that your fuel injectors are a bit clogged. You
can get them cleaned. It's an hours labor plus the cost of the
cleaning agent. The cleaning agent comes in a canister that
you can pick up at your local automotive supply store. If your
mechanically minded you can attempt it yourself.
I was also going to suggest changing your fuel filter, if
you have not done so already. I know you said that your
MB dealer did all maintenance and tune up, but exactly did they
do. Not to cast doubt, but make sure they itemize what they
repaired and replaced.
A friend who had the identical problem on his 260e thought it
my have been his fuel pump and he got it replaced. As it turned
out, all he needed was new spark plugs, wires, d-cap and rotor.
It started in second after that.
I hope this is of some help,