I have a 91 300D 2.5. Be careful, with vacuum connected directly to the waste gate, boost can go over 20 psi. My boost gauge only goes to 15 psi but the needle goes way past that with full vacuum to the wastgate. This alone can cause a lot of oil in the turbo input if the crankcase vent is hooked up correctly. Excessive boost causes more crankcase blow by, causing more oil in the intake system. I have my boost set at about 14 psi and everything seems fine. If you have black smoke, probably the ALDA has been adjusted for more fuel than needed.
Get a boost gauge and check the boost.

Paul

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84 500 SEL (307,xxx miles)