I put in a new starter (Bosch Factory Rebuild) in my previous 300D in the Summer of 2004. I since got a new (to me) 300D and put that starter into the new car (after the previous car sat idle for several months). Now this 18 month old starter does exactly what you describe. My theory is that the grease in the solenoid has gummed up and doesnt slide well at cold temps. (25F or below). In most cases when the temps are in the 20 - 25 range, there is only a one second or so hesitation. But if its real cold (5F), there may be a several second delay. So I usually turn the key hold for a couple of seconds, then turn off and try again and invariabley, the thing turns over!!! Exactly as you describe. I think that the solenoid heats up when it doesnt engage, melts the grease, then starts fine. If this condition is not fixed, I assume the solenoid will burn out. I plan on fixing this soon....I did buy a new solenoid which I will put in...(I dont want to clean solenoid, regrease with synthetic, and re-install only to find the same behavior, although I am very curious to do this!!...thats why I got the new solenoid) I will check the condition of the grease in the old solenoid and if its gummed up, I will clean it and install on a spare starter with bad solenoid (from previous car). I will post followup.

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)