Why is my beetle not starting?

I have a 1975 VW beetle which I have owned for over 15 yrs. In the last year or more it
is not always starting. I have an auto electrician look at it as well as my normal vw
machanic look at it. No body can find what the problem is or it starts when they go to
look at it. The battery is fine, when I turn key on they oil light etc goes, turn the key
and there is nothing, n o clicks or noises. I can walk away from it and go back 5 mins
later and it will start or if not just push start it and it starts really easily. It is totally
random. It will go for weeks then all of a sudden not start. It is getting really frustrating
as I can never tell when it will do this. Any ideas??