The difference is in the size of the threads. Different year engines have different size freeze plugs. You have to remove the freeze plug to install the new block heater. Get your production date or Vin and call Phill at the 1-888 # at the top of the sreen...He will send you the right one.!!!
I have one in the wife's e300 D and she loves it!
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS