Ah.........Diesel Engine time; There are so many variables. The tack could have been replaced or not functioning. It all depends on how the boat was used. Thirty eight hours a year does seem a little light but not totally out of line as the boat may have sat for a few years.
Most tacks will only record true actual hours when operating at full RPM. Recall that tack time is not 'Hobbs' meter time. (actual hours the engine is running)
If it were me, I hire a diesel mechanic for an hour to look over the power plant and give you his gut feel on the condition of the engine. An experienced mechanic can tell you quite a bit in a short time,. It would be worth it - considering the expense of a new or rebuilt engine. A well cared for diesel engine should last you a very long time.....4-5 thousand hours....providing it has been cared for.

I learned the hard way that low hours can also be a bad thing. If a diesel have been babied, not run hard and hot this can be trouble too. My previous boat was just motored enough to get out of the slip and then sailed. Super low hours versus years old. Engine turned out to junk because it never got hot.

As it has been already said, spend a few bucks and have looked at by a expert. 

Does it start on the first push, is there any smoke and how does it sound?  I agree that low-hour diesels are not like low-mileage cars.

The babied ones tend to overheat when pushed so make sure you get it out on the water and run it at 90% for a bit.

I bought my boat last spring which is a 2003 (hull #2122) with only 225 hours on the engine.  Some owners don’t use they boats much.  Most knot meters also have a permanent log for the distance covered.  Mine showed less than 600 Nm.