Hi there,

When we got our '74 280C it was using great quantities of oil and would foul the #1 plug quite often. I finally noticed that the vacuum line going into the vacuum pump was clean but the one going from the pump to the intake manifold was very oily. That's right, the vacuum pump had a hole in the diaghram, and every time we went down a hill it would load up with oil and smoke like crazy. What I did was just remove the pump, it's not necessary anyway, and M-B got smart and removed it on the later year vehicles also. You might check your engine and just see where the line from the vacuum pump is plumbed into the intake manifold.... assuming it has a vacuum pump to begin with. Otherwise, I would suspect valve stem seals first, then rings. You can check the rings by doing a compression check. Worn valve stem seals usually cause an engine to smoke when it's first started after sitting for awhile.
Good luck with it, they are nice driving cars...

Richard Wooldridge
'82 300D/4.3L V6
'74 280C
'77 Jag XJ6L
'77 280Z