Damico I owned a a 89 300 E.
Heres what I think is happening Makes sure you replaced
the cap and rotor very important on old 103 engines if you
did that remov them. Heres the case I think from my experince as a factory techWhat Ive seen is arching going
on from the rotor arcs to the backing plate in Back of camshaft(that the little pole piece that holds rotor on.
take it off then the remove the allen bolt take that off.But before you do that spray some WD or liquid wrench
to loosen that allen bolt up I belive its a 6 mm they
strip out all the time. Once removed replace that shield or backing plate . I saw that happen, you be surprise its the less costly **** that goes wrong hope it hleps
Factory Certified Tech 14 yrs.
1993 500E 85K