It's possible that the gasket on the vac pump has failed, allowing oil
to seep out.
Check the front screws in the chain case (small ones on the front side)
as they can work loose and allow oil to seep out of the gasket there
without any leakage between cylinder.
I suppose a small leak at the valve cover would travel down there,
ditto for a leak from the intake manifold (boost pressure can push oil
out the bottom of the runner to head interface, and it will drip down
around the vac pump if it's the #1 runner). Might check for a drippy
crossover pipe, too, for that matter, as they always leak sooner or
later.
Everything else I know of that leaks is on the other side.
You've reminded me to check my 300D for the type of vac pump I have --
I hit 230,000 miles last week.
Peter
