I was having the same problem with my 1990 300E, perhaps less severe. Luckily I had the visual indicator of fuel dripping in the area of the fuel pump, and I replaced the pump, washers, and the line that leads into the pump from the tank. Since a buddy of mine runs a shop I got the parts at cost, and since then I've had no starting problems whatsoever....in fact I'll be adding an automatic starter to my alarm system tomorrow or sometime this week
hope this helps...
1983 300D 200k+ (stopped odometer)
1990 300E 123k
1999 E430 12k