The Vacuum Pump pulls from the entire vacuum system.....Power Brakes, ignition shutdown, door locks, and AC/Heat valves...and then some.....the Vacuum Pump discharges into the crankcase......so if you have a large vacuum leak....or maybe several small ones......you could be pumping air directly into your crankcase......

I believe that the engine should run under a slight positive pressure....so that "O" ring on the dipstick, is important as well......

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG