at the extreme end of things...i just pulled an old d50 diesel out of the woods. 13 years sitting. lucky the tank was 3/4 full, no issues with that. i removed the glow plugs and squirted some oil down there and turned it over by hand a few times. got the starter put on (turns out this was why it was parked, broken pinon gear), and new bolts between the tranny and engine (for some reason they were missing).
going good now.
as an aside...i use an old electric fuel pump to prime the main pump.
i am also a boater and we lay up diesels all the time for winter. here is a good link. most of the issues are fuel related, but note the recommendation to change oil at time of layup because of acids in the oil.
http://www.practical-sailor.com/marine/ ... ation.htmlcharge the batt once a month. i have had good luck with stabil.
tom