BMW Repair: ignition problem 525i 1990, fuel pump relay, bmw repair

Question
I have a 1990 525i.  I am having an intermittant problem of the car not starting.  There is no pattern to when the car won't start.  I have changed the spark plugs, cap, rotor,  checked the ignition wires, igniion coil and the comp relay(I think if it is next to the fuel pump relay located on the passenger side under the cover with four screws just to the left of the fuel pump relay) and the fuel pump relay.  The car turns over great.  When the car turns over when it won't start there is no spark at the spark plug.  I have taken it to a local bmw repair place and both times I have taken it there the car starts fine.  They seem to think it might be the ignition switch.  They told me unless it doesn't start while they have it they can't find out what is wrong.  I went to p/u the car this evening from the shop and it wouldn't start.  Have any ideas.  Thanks Jeff

Answer
The shop is on the right track considering that when it does start it starts fine.  Have a mechanic take it home with him or use it for parts runs, it's bound to happen when they are using it; so they can check the output voltage on the ignition switch.  the only way to diagnose a problem like this is to catch it when you have your voltmeter and know what wires to test.
-cheers