Only marine diesel experience I have is a set of Perkins saber engines in a 90 foot cat. They would come up from cape horn to Baltimore for the parade of boats. I'd get to do the pm on them, check the overhead, fix anything minor on them. (Just the engines) always got a good meal from the on board chef before I left. One of the highlights each year for me. Other then that, everything else I've worked on has been gas powered.You should try the marine world. We have to buy parts for our big in-line 6 Yanmars through Detroit Diesel, and parts for our little 4 cylinder Yanmars through John Deere, despite the fact that we've been a Yanmar dealer for 30 years.
Don't even get me started on the Westerbeke/Kubota relationship.