Starting problems LDV Convoy 2.5 Diesel 1998?

I have a LDV Convoy 2.5D dropside 1998 van sometimes it will start first time and sometimes it starts then stops after a second or two. A garage has looked at it and they say it's the Engine Management system (which because of where it is placed is damp and moldy). Is this likely to be the problem or is there another solution. I've also been told that to solve the problem, would be to either replace the engine with a bog standard 2.5 diesel or spend money on a new EMS and a new fuel pump. Please help