Engine won't start suddenly having been fine..

[tom fleming]

My ML 270 cdi (austrian build, year 2000) had a new set of injectors and performed very well for 3 weeks. Great pull, minimal smoke. Parked up briefly one day so engine hot but on return she suddenly wouldn't start. Went through two batteries (had spare in back) over a couple of days but no luck. Turned over fine, but apart from brief moments when she seemed to fire, she flatly refused to start. I noticed bubbles in the fuel lines and replaced the washers with new ones (MB). Made no difference. Crankshaft and camshaft sensors were replaced in last 9 months so guessed it wasn't them. So called up the rescue truck and she was hauled aboard and taken to my local garage. On arrival at garage she was unloaded. Mechanic jumped in and tried to start her. Burst into life as though no problem at all! He took her for a spin and stopped a few times to make her misbehave. She started every time on the nail. (cheeky b*tch) Are there any wise heads out there who might advise me as to what might be going on? I'm a tad nervous and want to head to Cornwall soon from London. I should finally mention that the garage did register low fuel pressure though she seems fine right now. I'd be grateful for some tips. Many thanks..