As time allows put in a new diaphram in your vacuum pump. My first Benz was a 1980 300CD. Well the diaphram failed and sucked oil up into the air breather and into the vacuum lines that fed into the passenger compartment. What a mess.
I knew absolutely nothing about these cars, but learned over the years by exploring Pic N Pull junk yards.
I eventually bought a shop manual on CD from Ebay that covered this car. And the three Benz's that I have eventually come to own since then.
I also discovered that putting 8 oz. of Marvel Mystery Oil in the fuel tank at fill up would give me around 47 more miles per tank! Every little bit helps.
Good luck!