You should use Premium. It should say that on the dash by the gas gauge. My 1990 300e does. Hope this helps.
I have never had a problem with Regular gas instead of Premium in my 87 300E. As long as you have a good strong spark and clean fuel injectors. I would recommend "Bosch Platinum +2 Spark Plugs" they have twice the spark so you will feel the power increase after you replace your pugs.
DexIII/Merc
The 1989 Mercedes Benz 300E came equipped in a 3.0L L6 engine. It has a canister type fuel filter which will be located underneath the car and forward of the fuel tank in the fuel line. The OE replacement fuel filter is Fram #G3737.
Located just left (looking into the engine) of the fuse box on driver's side. It is a canister type. Mr. G.
"ATF" or standard automatic transmission fluid. The bottle will say "ATF" on it, and is available at any auto parts store and most gas stations.
Corp a
Whay type of model do you have? 300E
The 2010 Mercedes-Benz Sprinter has double overhead cam (DOHC).
The 2011 Mercedes-Benz Sprinter has double overhead cam (DOHC).
The 2012 Mercedes-Benz Sprinter has double overhead cam (DOHC).
The 2013 Mercedes-Benz Sprinter has double overhead cam (DOHC).
The 2014 Mercedes-Benz Sprinter has double overhead cam (DOHC).
Mercedes-Benz