Intermittent starting problem

I also have a punto with a starting problem which is intermittent. It has had new coils, new battery, new wires etc. When it wont start it turns over fine but just doesn't seem to fire up. If I leave the car and go back to it later (sometimes an hour later will do, sometimes a day later) it usually starts up fine. It doesnt store any fault on the diagnostics and has had both RAC and several garages/mechanics look at it but as the fault is intermittent it also often starts again by the time they get out to it so it is hard for them to know what to say as they dont see the fault.

Once it didnt start at all over two days and so the garage came out and towed it and then when they unloaded it at the garage they turned the key and it started first time. There can be anything between days or months of this fault occuring for example three times last week, but before that a month between, prior to that about six months between before that twice in a week etc it is random and unpredictable and not seemingly linked to weather conditions either! I have had this car for two years and spent a fortune tryign to fix it. Each time I have had something replaced and the fault hasn't occured for sometime I think it is fixed but eventually the fault occurs again. Now I am looking to get rid of it once and for all, unless anyone can help me with a solution....?