[patrickt]

I've seen a couple of MSD boxes go bad, but not very many considering how many are actually on the streets. But I can't say I've seen an MSD box go "intermittently bad." It usually either works, or it doesn't. Before you blame the MSD box, undo all connections to the box and clean them (the big red, big black, and skinny red particularly), check your rotor and cap, and try wiggling stuff with a light on the skinny red to see if you can make it blink. I had an ignition switch that was misbehaving on my Cobra and the only way I was able to find it was to put little 12v lights on every step of a circuit and when the misbehavior occurred I could see what lights were lit and what weren't). The MSD pickup in the distributor (assuming you have an MSD distributor) usually fails completely too.