I would be concerned on the lack of maintenance and how long he has maintained the vehicle in that manner. Regular oil changes are critical on the car. As far as what could have been impacted in during this one time (if its only the one time) is hard to tell, depending how low. Obviously, less oil adds to the wear and the potential if low enough, for un-lubricated wear items. I am sure you know all of this already.
The engines are pretty solid and a one off might not be that big of a deal, but usually a one off is an indicator its been done before or that the owner doesnt really care about the car anymore and will neglect / treat it like a beater. (Like a rental car ;-) )
he's actually got very detailed records up until that time. He showed me his binder and it's very thorough. That's why I was so surprised. I guess stuff has happened the last couple years for him, I'm not really sure. I know he had a kid and moved.. anyway.
18k miles? The 10k mile intervals are conservative. Blackstone has seemed to find that, for most, 15k would be OK (not optimal). Running low isn't good, but it kind of depends on how low. If you're still reading in the hash mark area after 18k miles w/no added oil then I'd have to say that things are probably pretty much OK. Obviously, you'd want to change EVERYTHING right away.
Yeah, the mileage was fairly low for 2.5 years so I was a little relieved. The oil level when I checked it made me a bit nervous though. It was below the lower bend. He said he's never added any oil since the oil change. I just spoke with him and he said he drove it tonight and at one point the oil warning light flashed on and beeped, but then went off. He's since added oil (not sure how much) and he said it's back within the hash marks. I'll ask him tomorrow how much he had to add.
The price he's asking is great. I'm not sure where the oil has gone since there's no evidence of leaks that I could see. I think there's a guru near him, so I sent him the list and told him to call.
His last TB change was at 163K. He said the first tb job he had replaced with the 100K mile parts but had forgotten when he had the next one done. The car has 183K miles on it. No rust, no upgrades, all stock. He said he'd sell to me for 2500. lol. I can't pass this up.
When you say everything, how deep a rabbit hole is that exactly? Are you talking replacing the normal maintenance items? Should I remove the valve cover or maybe even the head and check for any damage?
He's taken his car to the same guy for everything (except oil changes when he did them lol. he did those himself he says) and though this guy isn't on the forums here, supposedly he only works on vw/audi/porsche/mb/etc. but he said he has a few TDI's himself and has been working on them since mid 90's... I know that doesn't mean he's been doing good work necessarily. As my coach said "Practice doesn't make perfect, practice makes permanent"
at least he hasn't taken it to the dealer.