1997 Nissan Maxima Electrical/Starting Issue

Alternator and starter have been replaced in the last 8 months (they actually had to put a 2nd alternator in because the first one was "bad"). Starting about 6 weeks ago, every couple of weeks, the car will not start (no engine reaction whatsoever) even though all lights, radio, etc. Work fine. Generally, it will start on the 2nd try. However, last week, it took an hour of waiting before it would finally start. Mechanic could not find the problem even though he said they have a great electrical guy on staff- he was only able to duplicate the starting issue once - said that alternator/starter/battery are checking out fine. He basically told me that I will have to wait until it again won't start for a long period of time and then they can test. I hate to get rid of the car over this but it is worrisome to have a starting issue that can't be figured out.