I was JUST about to tell you to change the spark plugs lol! My 300SEL used to be VERY hard to start when cold...sometimes I thought I might be stranded even. Changed the plugs...no more problems!
One must wonder why your plugs were bad though...my M103 kept fouling plugs because of excessive oil consumption, and would lead to this really hard starting problem, which, if let go would turn into a misfire and hesitation.
I would keep a close eye on your oil consumption.