Mine is a 1984 380sl with the round plug. I have talked to several mechanics and none have any idea what we are dealing with. Its too old to be OB11 and maybe too old for OB1. I am about 90 miles from from the nearest dealer and don't want to go there anyhow since they don't want to work on anything over 10 years old unless they sold it. I had a good mechanic but he retired and sold his buisness to somw people from the mideast and I have not had very good luck with them. The last time I went to them they charged an arm and a leg and still did not solve the problem.