I am looking at a 1980 300TD wagon tomorrow. 178K miles non-turbo 617.

My concerns:

This car was passed over by another potential buyer because of the oil pressure. I asked the owner to start the car. At warm idle oil pressure was 1.5. I asked him to rev it to 2k rpm and he stated it read 2.5. Is this something I should be concerned with or is this normal?

I will of course check for blow-by.

I am also concerned when the owner mentioned that in the back of the car is a empty oil container by Quaker State that read 10w-40. This car belonged to his father who he said was a Mercedes enthusiast. This does not seem to be a diesel motor oil. I am hoping it was just back there to throw away and not used in the car. However if this car was run on non-diesel oil what should i look for besides blow-by?

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Current Cars:
1980 300SD 201k daily driver
1960 190D 468k My Dad's car i hope to get running 1 day
2004 Acura TL 3.2 32k
1997 Honda Civic 63k
1989 Jeep Cherokee 166k
1960 GMC 1-ton 4x4 350ci v6 56k
1984 Ford F350 150K 1-ton crew cab dually
1976 Ford F350 157K crew cab 4x4 w/354 Perkins, Clark 5spd, Browning 4spd