I had/have same issue on a 1992 300CE m104 engine. I changed spark plugs and gap, and it didn't make much difference.
I plan on looking into it more, but for me its not a big deal. I think mine is caused by the injectors leaking down.
If I turn off the car, it will retsart on first try if I start it within a few minutes, let it sit for 10-20 minutes or more and I have to crank it twice.
Cold starting starts fine.
I talked to my mech about it and he thinks it might be the injectors leaking down as well, since the car runs smooth as silk when its on.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.