Car won't start

I have a 1997 520se, a month ago the car wouldnt start, the garage had a look at it and replaced the spark plugs, the car started. but several weeks ago the same happened and the garage had another look at it, and got it started, I asked them to carry out pressure leak checks on the injectors and a diagnostic tests but couldnt find any thing that would stop the engine from starting. There was a spark, and fuel getting to the chamber. A BMW man suggested it could be a problem with the block liner allowing fuel to leak through. Any ideas.

My car won't start at all. Mine is an 85 528e; it has gas running (i replaced the main pump) and I checked for ignition coil resistance which was good and I checked one of the spark plugs and there's spark. I really don't know what it could be; I read the book and it says that the timing is not adjustable on my car, something with the ECU which I haven't checked because I can't find the plug.