Change fuel grade to mid or fuel regulator sound like easy tries. I thought I read in the archives something having to do with fuel injectors?
I am having a similar problem w/my 95 E320 / 132K miles... cold it starts with no problem.... if I have been driving around and try to start it when hot, I have to give it some gas , which is odd since a fuel injection car is not like a carb car...but it does start easier, with less cranking over (cranking over is normal not slow /battery)....
I know the problem is easily fixed... drive to local shop, they'll fix it, and it will be about $300-$400
... LOL