Hi upod,
Thanks for the questions. Assuming you understand how the pneumatically governed injection pumps work, you know the importance of having a sealed governor system that will hold vacuum. A vacuum leak in this system leads to over-fueling. If you find that one of these governors will not hold a vacuum the culprit will likely come down to a leaking diaphragm and/or a worn adjusting shaft and the bushings it rides in. In my case it was the worn shaft (see the link above, in post #1). Furthermore, though I cannot say with 100% certainty because I messed around with other factors, I am fairly confident that I almost destroyed the engine in the '74 240D because of the leaky governor. See this:
Pre-Chamber Ball Came Loose
When I bought the '74 240D it was running OK, but never quite as good as the '73 that had a completely rebuilt OM616.916 engine I bought from Metric Motors and installed back in 2005 or so. Compared to the '73, the '74 just wasn't as smooth, and it nailed and emitted grey smoke that smelled like fuel, especially when cold before reaching operating temperature. Even at full operating temps the '74's engine still had some "rough edges" and tended to emit grey smoke. Power output at mid-throttle cruising was a little "bouncy", inconsistent. Checking and adjusting IP timing, and installing rebuilt injectors, didn't resolve the issues. But the car ran "OK", so I never dug into it, just accepted it, until the engine almost died.
I don't have any videos for you. Dyno numbers? Nope. This isn't really an optional, "maybe I need this", "maybe this will get me better fuel economy" kind of repair. You either find a vacuum leak at the adjusting shaft or you don't. Primary benefit to the owner of the vehicle is, essentially, a properly functioning injection pump that delivers the right amount of fuel. Benefits to the shop mechanic include the ability to make a good repair without having to resort to other workaround type solutions.
Testing the governor is easy. If the diaphragm leaks you will feel vacuum or pressure at the IP's oil filler neck. In my car I could hear the vacuum leak, and feel air coming out from around the inner end of the shaft with a little pressure applied to the housing. I used soapy water to verify the location of the leak. I could feel the shaft's side shake, as well. The shaft had so much play that fresh o-rings did not fix the leak. One way to isolate a leaky shaft and rule out a leaky diaphragm is to apply a bunch of grease to the o-rings and see if that temporarily stops the vacuum leak and improves engine performance.
Installing the new shaft is easy and fast assuming you have all the parts on hand before you tackle the job, probably an hour or less. The injection pump stays in place on the engine, no need for re-calibration of the pump itself, though checking injection timing might be a good idea as a matter of course. The only part you remove from the engine is the rear-most housing on the back of the pump - disconnect the control rod and remove two screws.
If I've failed to answer your questions adequately please let me know! And thanks again for asking.