A MitiVac is a hand powered vacuum pump. Very useful for finding leaks, as it has a vac gauge on it. To find a leak, you would unplug the vac line in question from the manifold, then hook up the Mitivac and see if the line hods vac. If not, you can then trace back and see what is leaking. By this time, most of the vac servos and switchover valves/vac amplifiers will be going, the rubber diaphrams split.
Sucking a bunch of air down the left side will cause it to run lean.
I'd certainly check the left side manifold gasket for leaks, ditto for the seal. Very easy and cheap.
On the D-Jet there is a Y shaped hose from the idle valve to the manifold. One leg of the Y goes to each side of the lower manifold chamber, so if the left one was cracked, that side would run leaner thant eh other. Don't remember if the K-jet engine has the same setup or not.
I think it you have the cam one tooth fast you might be OK, don't know about one tooth late. Easy enough to check, just pull the valve covers and align the cam mark with the cam tower mark on the right side and see where the crank pointer and the cam mark on the left side is.
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!