I agree with Chuck, don't mess with the leak between the cam housing and the head unless it is really bad. I had a 126 280SE for many years, and it always leaked at that joint, even after I re-assembled after a valve job w/ the foil gasket.

My car was also federalized very poorly. The generic O2 sensor will work; or you could just remove the added stuff for "testing".

__________________
as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5