Guesser...I'll jump back in here for a moment. Additional thoughts beyond what has been covered above.
1. Too many hours is always a problem as things DO wear out. Fortunately with diesels..this is generally many thousands of hours of use before significant wear occurs.
2. If you are only using your diesel 10 minutes each way, you are probably not getting it up to the 180 degree operating temp it needs to keep itself "springtime fresh" internally. Be sure to get it up to temp when you use it or you will surely pay the piper down the road.
3. A low hour 30 year old engine that has been run regularly up to temp and meticulously maintained would be almost as good as a brand new engine. And you will find one of those engines right after the tooth fairy puts a quarter under your pillow! The best you can generally hope for is that their is only minor and fairly inexpensive benign neglect.