Could be a restriction in the fuel
system that forms a bit of a vacuum as the engine
is run. When you go to restart it the engine is suffering from fuel
starvation and needs a lot of cranking. If this is the case, after the engine sits for an extended period, the fuel seeps back in and the engine fires right up. I'll qualify my answer by stating up front that I'm not a mechanic
but I have read of similar problems. My diesel
education is limited to keeping a 30 year old clunker going for longer than it wanted and then replacing it with a new 3YM30
(which has worked perfectly).Good luck!