Your right about it being older and being an engine that has been sitting for a while, it could possibly have issues with rings and bearings like every other engine out there. It hasn't been started except by the factory when it was tested and sold. I'm not trying to get rich off the motor as i'm just trying to find somebody that would put it to good use and get a fraction of the money back that was spent on it. A rebuilt motor of the same model that uses a 20 yr old block goes for over $8,000 and that's usually just a long block without the starter, turbo, radiator, etc. John Deere engines are very sturdy, parts are readily available and reasonably priced. An in-frame overhaul kit which would replace most of those questionable parts can be purchased for around $900. Most new 4045tf model diesel engines made by John Deere go for well over $15,000.
Id be willing to take less just for the doubts on the condition of the seals, bearings, etc. Enough to by a rebuild kit if necessary and have a fresh, NEW engine...not an old used block with a few fresh parts.
Id take $8,000 just to make room for possible issues