Any air leaking into the intake manifold that does not go through the mass air flow sensor is a vac leak.

The AC system, the transmission shift harshness control, and engine controls are all vacuum powered, along with the brakes, so a leak in any of them will give you out of control lean mixture at idle (rough running) and low vac in the manifold. This will produce the hard shifts (and remember, MB trannys don't slop form gear to gear like a GM slushpump -- that's why they go 300,000 miles rather than 90,000). The AC vents will close under acceleration if the leak is pretty bad, or the mixture is too lean.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!