Cadillac Repair: Northstar misfire in my Olds Aurora, 1997 oldsmobile aurora, oldsmobile aurora

Question
I'm actually writing about my 1997 Oldsmobile Aurora, which has the Northstar engine.  About a year ago, the check engine light started coming on in the morning (every now and then), but it would go off after a while.  Eventually it started to misfire now and then. The readout said cylinder 1 misfire so I changed the cylinder 1 coil pack.  It ran fine, but the check engine light came on once (seemed to be running find) and a couple of days later it rained heavily and started to misfire badly.  The code now said multiple cylinder misfire.  I changed all the plugs and wires.  It then ran great and fine in a moderate rain, but again in a bad thunderstorm (big puddles everwhere) it started misfiring badly - so badly it stalled and couldn't be driven.  Had it towed to a garage.  They were unable to duplicate the problem (though they charged me to look at it) so I took it to a Cadillac dealer.  All they can find is what they called "lazy oxygen sensors" in the exhaust.  What could be going on?!

Answer
Obviously the coil packs and or the ignition module is getting wet. I would purchase a spray can of silicone spray and coat evry plug wire, the coils and any electrical connections at the coils and ignition module and see if this helps.

It is very difficult to diagnose a problem from where I set as it is for a technician can when the vehicle runs perfectly when he sees it.