If your vac pump has two tubes, one to the intake and one to the brake booster, you have a diaphragm pump.

Now, is the tube going to the intake black and wet with oil inside? If so, then your vac pump needs some parts, as previously discussed. If not, your problem has nothing to do with the vacuum pump.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).