hi everybody i am a long time reader new member based in northern nevada

o.k i need some help and advice here please

please bare with me i am trying to give details. there is a related post but as usual with forums some clueless explanations and no conclusion

ok so i bought another 1985 mtd w126 ca model turbo diesel om617 5 cyl
for use as a daily and then later a donor in a swap

it was parked unused for several years. the glow plugs were dead and i was / am reluctant to start them on ether starting fluid (i use a diy safer aproach)

so this time i simply cranked the motor just to build a good oil pressure then let it sit then re cranked it let it sit then started it up properly knowing it had oil circulated

it smoked a lot ( expected) white but imediatley idled nicely i drove it back n forth on back roads for maybe 20 miles it drove fine shifted fine and the smoke cleared.oil pressure was fine temp was at normal. it was sluggish off the mark but i put that down to filters and smog bs and a high ratio and auto box in a heavy w126

however it did have an intermittant ocasional tinkling rattle somewhere if you really listened which sounded like a loose bolt or something in the tc but nothing significant or with any clockwork rhythm. oil pressure was fine litterally like a bolt vibrating around on a tin tray ocasionaly

i brought it home ( trailer) and began to make plans for it ocasionaly starting it and noticed that this intermittant rattle would sometimes sound like a tinkling noise and sometimes not exist and sometimes sound more like a grating grinding noise similar to a very bad water pump or alternator bearing but i could not isolate the noise. oil pressure was fine. switch off re start
it starts right up ( temp not even off cold) and the noise has now vanished.

i attempted to turn the car around so i could test the c.r in my garage before i got too carried away with my ideas . oil pressure is fine and next thing i notice the oil pressure is now suddely just above zero temp is still cold as it wasnt running long. there are no oil leaks

i imediately switched it off there was no noise no bottom end rattles. i recheck oil level and its in the safe area so i add some but knowing it probably wont affect anything.
but even if i just try cranking it ( short bursts) it wont make oil pressure.
and now i am reluctant to do a c.r test by cranking in this condition.

so.......

i am thinking its got to be an oil pump / delivery issue and maybe that was related to the intermittant noise? BUT

is this an easy fix? drop the sump and swap in another pump or drive shaft???
( never had one apart to know)

do i carry on and adjsut valves if needed and do a cr test anyway?

or should i simply pull anything usefull off the engine (what?) and part out the car or sell as is to an enthusiast explaining the issue?

i have a few projects and dont need to be going backwards right now
the car is rust free very straight and nice interior

usefull helpfull replies are very welcome. i am sure this must have happened to others?

thankyou for reading and i hope i can repay the advise sometime