My 300TD did exactly the same thing back to the previous owner (a friend) years ago. A new starter cured it.

He'd taken it to the airport and when he returned the valet couldn't get the car to start. "Sir, is there some special technique to get your car to start?" He had to go out into the yard and spend forever to get it going. The lived with the stupid thing for weeks until it got cold and was almost impossible to start.

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Sadly Benz-less