How to fix distributor cap from getting wet - GMC Cars & Trucks

Shouldn't have to replace it. Just take it off any let it sit to dry it out. I've sunk one of my trucks and the distributor got wet and it was fine after letting it dry

Water on the spark plug wires will do this, especially if your car has a distributor that is not solid state. Water gets inside the distributor cap of the older vehicles and shorts the spark to other cylinders than the ones intended which causes the rough running.
To push the water off the wires and out of a distributor cap, spray WD-40 anywhere you do not want the water so you can run the vehicle. Be very careful if you do this inside an older cars distributor cap since The WD-40 will also break down the bearing lubricant down the shaft. Use this in an emergency to get you home etc, then see a mechanic to make sure you didn't cause any bearing issues.

If this is a petrol engine and if it is at its worst in wet weather then you may have a spark plug lead problem or crack in the distributor cap. Run the engine when stationery and view the spark plug leads and distributor cap at night in the dark and get someone to rev it up and watch for sparks around those areas, New leads or cap will be required.

Let's start with the basics. Did you notice any wetness in the distributor cap? or wetness in the coil wire boot at the coil? if you saw wetness in the distributor cap? You have a cracked cap and spark would be sporadic.
If you saw wetness in the Coil boot? The coil is bad. When the coil is bad the engine will stall when the coil gets hot. Also check and make sure ground wire from engine to firewall is very tight and clean. Actually any connection can be lost if its dirty , loose or both. I would check wires (Plug) going to coil and distributor reseat them by taking the plug off and using an electric spray cleaner and blow them out with an air gun to prevent cleaner shorting out the system.
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Try putting some dielectric silicone grease in the boots on the spark plugs and a thin layer around the distributor cap. There should be a seal on the distributor that seals the joint between the cap and distributor. Park it in a garage and use a blow dryer in the distributor cap / distributor.

YOUR PLUG WIRES LEAKING OR IGNITION COIL PACK SOME HOW IS GETTING DAMP OR WET.

There is a drain in the distributor that gets clogged up and holds moister under the cap.It is like a vent .So i would replace the cap and rotor and check the vent hole the will fix the issue :)

why, idk. Where, well the only way oil could be getting into you cap is if for some reason it's coming up the distributor shaft. I've worked on many distributor vechiles and NEVER came across this problem. But there is a first time for everything.

Check your distributor cap for cracks. Sounds like you are getting condenstion under the cap.

Sounds like moisture is getting into the distributor cap. Try putting a thin film of petrolium jelly around the lip of the distributor cap where it seals down onto the distributor. This should stop the water from getting in.