I’m going to be freshening up my distributor for my 1950 Cadillac, and I think because of bad weather stripping and other leaks, when it rains heavy, moisture might be getting on the distributor. Is there something I can spray on it that will help repell moisture or would just a healthy dose of dielectric grease do the trick?
Replace the cap/rotor. It’ll come with a gasket that will seal the distributor again.
Depending on vintage, does your cap have a little port in it through which the points can be adjusted with a dwell meter? I have never seen a gasket under a distributor cap, especially in 1950…Distributors are usually located in a dry spot…There is a CHANCE that a newer HEI ignition (1975-1985) models will simply drop into your engine. Then all your ignition problems are over…I would investigate that…
Spraying the outside of the cap and wires with silicone might give some water protection…
I wouldn’t worry about it, just make sure you have all new parts, and when you take it out drive it long enough for the engine to get thoroughly warmed up. Cars with distributors and points handled wet weather just fine, even though engine compartments are not sealed against rain and road spray.
And I agree with @Caddyman - I never put a cap with a gasket on a US car that had points.
I don’t remember a gasket either but I might suggest changing the plug wires at the same time. I know I sprayed some kind of clear sealer (maybe silicone) over the cap and wires but never really had a weather issue anyway.
Moisture can get inside of the distributor cap no matter how tightly it has been sealed. The key factor is the dew point in the atmosphere.
Spray it down regularly with WD-40; especially at times of the year when it’s very humid or cold and damp.
Thanks guys. I’ve got new wires, rotor, cap, points, condenser, coil, and plugs coming.
Good. Moisture-related ignition problems can sometimes be caused by dirt and deposits on old cap, rotor, and wires.
The WD in WD40 stands for water displacement.
Unexplained moisture inside a distributor can sometimes be crankcase vapor getting past the distributor shaft seal…
D’oh. You guys are right about the gasket - I was thinking a few too many years in the future 
Of all the cars I have owned with a distributor and ignition points including a 1947 Pontiac, 1948 Dodge, 1950 Chevrolet pickup truck, 1954 Buick, 1955 Pontiac, 1961 Corvair, 1965 Rambler, 1968 AMC Javelin, 1971 Ford Maverick and a 1974 Chevrolet Monte Carlo, the only cars where I had moisture inside the distributor cap were the 1961 Corvair and 1968 Javelin. The problem was solved by replacing the distributor cap and wires on these cars. The 1961 Corvair was really interesting. It was’t running well when I bought it and the AMC dealer thought it needed a valve job. He said his mechanics didn’t want to work on the Corvair. I bought the car at a good price. We hadn’t had the car very long when we drove it to go out to dinner. While at the dinner, a sudden rain storm came up. After the storm, the car ran so poorly that I didn’t think I would get home I reasoned that the problem couldn’t be valves as wet weather wouldn’t affect the valves. I replaced the distributor cap, wires and spark plugs and that Corvair really ran well after that. It didn’t need a valve job at all.
Good to know thanks. This is my first old-school car so I’m going through the learning curve. But man, I love these old things, watching them come back to life.