I was hoping a real diesel person would be weighing in with more here. But have you actually checked your valve clearances, as someone else suggested? All you need is the right thickness feeler gauge, a spanner, and a screwdriver. I think all does usually look beautiful under the valve cover, but that doesn't tell you if they're adjusted correctly.
2000 Beneteau 331
Northern Chesapeake Bay
Ambition is a poor excuse for not having enough sense to be lazy ~ Steven Wright