1995 320SL: I had the head gasket replaced recently by a local mechanic- bad oil leak. Oil leak fixed perfect ! - but now I have no 5th gear Overdrive - other than no 5th transmission shifts perfect 1-4. My mechanic said issue not his fault - but advised I need a new ECM circuit board part # 016 545 62 32. Anyone else had this issue, and advice on source I can trust on the Electronic board?