Now before anything can be answered, what type of "long" cold start are we talking about?

Is it cranking over but not starting at all the first time? Or is it just cranking a couple/few more times than usual? The oil grade also has an effect on a cold start. If you have 0w-40 in the motor, you shouldn't have any issues. If you have 5w-40 in the motor, which btw is fine for our engine, it might crank a bit longer on very cold starts.

For my last oil change, I actually had 5w-40 put it from Mobile 1 by my local Loeber Mercedes dealer. They knew it was the same motor as the SLK so yeah. 5w-40 takes longer to crank on very cold starts, but so far mine has been fine. I will go back to 0w-40 before winter hits here in Chicago.