I do not think the loading / unloading caused that, since the lugs drive only the main oil pump and have no idea of what horsepower is the engine pulling. As for anything getting inside there is very dificult to happen. I saw the pump cresent worn out badly, so my opinion is the the converter was maybe "pushed" not in alignment sometime when "they" worked on the engine or trany and bent a little the lugs. These in term worn out the bushing and the rotor (gear) part of the pump rubbed often against the cresent. With time the bushing wore out more and one lug broke remaining basicaly "in place" helping the pump gear to be "off center" and wore it more to the point there was no working pressure.
I have better pictures but cannot load them on the board. If interested send an e-mail to me and I will return 2 o 3 pictures. (WFGonzalez2@cs.com)
Right now I swapped the trany for an 1983 240D trany with vaccum modulation. (Bad luck, I have no vaccum modulation in my 1976 since the engine "load" is conveyed to the trany via a physical linkage from the gas pedal. So.... I am driving around with a hand pump utilized for testing vaccum systems in gas engines to simulate the engine load, basically 6 to 20 inches of mercury.
I am still happy with my "new" puppy, I just bought it with a brokent trany, but learning to deal with diesels for the first time in 66 years.
The unsolicited story (after I purchased it) about the mileage from the previous owner was that he bought it in Florida from the 1st. owner just a while ago and drove it to Texas. The engine has a lot of pep even on uphills, but burns a little something that I cannot figure out what it is (smells like diesel), so trying to see what to do with it. My best guess is that I will take the engine apart, file a little the rods and mains to get the proper bearing clearances and with new rings and chain see what happens !!! WHAT IS YOUR GUESS WILL HAPPEN?
Back at the ranch, the original trany still on the bench (a piece of 3/4 playwood) with new set of gaskets and debating where to pay the nearly $600 they ask for a new main pump, or just braze the cressent (inside) then get it on the lathe and machine it to take the original gears (seem in good shape yet) and get the baby back on the road with the original mechanical linkage modulation, stopping the driving with one hand on the steering wheel and another on the hand pump !