I have 1995 E420 with same problem. It had hard starting problem, I took it to the mechanic and he replaced my battery. But the problem didnt go away. I have replaced by distributor caps and rotors, and spark plugs. still the problem doesn't go away. I have also replace my fuel pump check valve after diagonsing the the fuel pressure. The check valve were bad I replaced them it had improved the starting but there are some other factor affecting the starting I am still working on fault. My mechanic said it is normal for the car with this much mileage to start in 4 to 8 secs. If it goes beyond that then there is serious problem. My car also runs smooth after it starts.
Things to check for :
1. Check battery voltage with the car off.
2. Check Fuel pressure with fuel gauage. I will give u test procedure later on. this will tell if any fuel pressure is leaking.
3. also check ur distributor and rotor conditions (watch for traces and broken distributor cap)
4. check ur spark plug wire.
I am researching one more thing that is electronic throttle control. If i find anything i will update you.