I was all set to say that it's the tensioner o-ring seal. Are you sure that's not it?

That, the cam cover gasket. cam box gasket, and front main seal are all that I am aware of that could cause this.

The crankcase ventilation is mid-way on the driver's side of the engine. You should see a tube from the intake manifold to the cam box. You remove the valve cover and it takes a giant screwdriver or flat piece of metal to remove it.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe