Oil pressure gauge

[UriahT]

So I just bought a great 1985 300CD. During the test drive (warm), the oil pressure read 1.75 then pegged as soon as the go pedal was hit.

A few weeks later when I picked it up, the oil pressure gauge stayed at 0. Only noticed on the highway doing about 70. Drove it 15 miles or so then parked it while I waited for registration to go through.

Seems like there's only 2 options for what happened here:
-Oil pressure sending unit is a no-go (either the unit itself or in the train of thought leading to the reading in the dash)

-Oil pump is gone. Seems unlikely considering I drove it 15 miles without blowing the engine. But what are the chances of that happening? Temp gauge stayed normal, didn't hear any exploding engine sounds.

Going to pick the thing up tomorrow (and driving home 100 miles). What should I check here to ensure I won't end up on the side of the highway with a cracked block?