"After a bit of throttle persuasion. it will stumble some more. then slowly come to life, and run perfectly fine."

I had the same problem and the fuel accumulator failed the test. Search recent posts by me "fuel accumulator" on how to run this simple test on the car.

If yours has failed you're going to have a tough time finding a replacement until late May.

Mercedes may have stock, but the one that was supposed to be in the Fontana warehouse was not there, so it is coming in from Germany. Bosch will have no stock until late May.

M103s have hydraulic adjusters built into the end of the rocker arms.

Duke