Oil all over the bell housing only indicates that there is a very small leak and its splattering like that because of the wind from driving. If you haven't noticed a great deal of oil loss then don't worry about that. I think the oil pressure sender unit has an o-ring or something, I just replaced mine not too long ago (took only 5-10 mins) and everything is fine now. replace the sender unit first and go from there.

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1990 190E 3.0L