Yeah, I'd wager that the PM was completely neglected. I HIGHLY recommend Shell Rotella T6 full synethetic for oil. The reason is because diesel oils do not have the same restrictions on cleaning agents that "regular" oils do--so their cleaning agents will last longer between oil changes. For an engine that has been neglected, those cleaning agents may be entirely consumed in the first 1000 miles--at least with a regular oil. I change mine religiously at 3,000; have done it for several vehicles now--and it works great. I don't buy the hype about longer change intervals.

P.S.
The ONE thing I'd verify if they do a rebuild on your engine--is the oil squirters & passageways. There's a reason OEM engines tend to burn oil--and I can state factually that my own engine does not. I'm not sure if it's a rebuild--but I wouldn't be surprised.

p.p.s.
Unfortunately, you're also seeing one of the issues I've seen some of my car buddies run into by trying to buy on the cheap end of the market. That Corvette that is selling for 5 grand less than any other comparable model--is probably beat to tar. Fortunately, you're a handyman & can address problems yourself. There are many who aren't nearly as skilled--and they quickly realize that buying on the cheap end of the spectrum--in order to afford a vehicle they probably shouldn't afford in the first place--is a losing proposition. Kind of like how thinking you're approved for a $200,000 mortgage doesn't mean that you can or should AFFORD said mortgage.

Best of luck to you! Keep us informed.