As a diesel engineer I can say it is very important that engines are run up to temperature regularly or they will dry out the oil and water seals and leak. A 37 recently sold with very low engine hours has had oil seal problems. I would be suspicious of any diesel engine that has not done 100 hours per season. Its just like a car, they need to be used.
This advise is also relevant when laid up and out of the water over a winter. I run the engine from a bucket of water with a hose in it every 6 weeks until warm. New engine oil before layup is essential also.