Technical engine

[Encebras88]

I have a Pilote P600 2.3 multijet 130 motorhome. Last week on return from MOT station after a couple of clunks, the engine stopped. Taken to garage by breakdown and partially stripped to allow access to turn the engine. Solid. Had the timing belt etc changed about 5 weeks ago. Everthing fine apart from 3/4 occasions when it would'nt start first time, but then it fires up. Put this down to possibly dirty fuel, hence the service and MOT. Mechanic says the belt, tension etc is spot on and is going to investigate further. Any suggestions greatly appreciated.
Thank you in advance,
Robert