It would help if we knew if you have spark or not. Next time it's failing, disconnect the coil wire from the bottom of the distributor cap and lay the connector about 1/2" from a ground point (like the right strut mount bolt). You should get sparks when you crank the engine. If you do get spark, you probably have a fuel problem, check the relays per Chris. If you get no spark, I would suspect the crank position sensor on the top of the bell housing or the power stage(ignition amplifier) on the inner wheelwell by the air filter. If you have a small plastic box bolted to the ignition coil with one wire coming out of it and connected to the coil, try disconnectiong the wire. The box contains a capacitor for RFI supression. If disconnection allows the engine to start, throw away the box. The above assumes you have the Bosch ignition. I'm not familiar with Rex/Regina. Let us know the resolution.

Good luck,
Bruce
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'88 745, '87 744 in Virginia Beach