I live in an area of NorCal with generally high relative humidity. I’m working on the distributor of a '90 GMC S15 Jimmy. When I took the cap off. There was a significant amount of corrosion/rust around a lot of the components. The auto was running very rough.It would run,but no power. I’d narrowed the problem down to the distributor cap/rotor,correctly. Would it be wrong to waterproof the cap when I replace it? I’m thinking a simple gasket seal around the cap/distributor interface.
My '75 Civic and '81 Accord had gaskets like that.
Maybe run a bead of Permatex(?) around the distributor where the cap mates.
I don’t see any harm in it.
Spraying the cap down, in and out with WD-40 will help shield the cap and rotor against moisture.
You can also obtain a rubber distributor cap boot from an 80s/early 90s era Ford Taurus or Sable with the 3.0 and see if that will work on your Jimmy. A salvage yard should have one of these on the dirt cheap or for free.
These boots were made just for that purpose and if for some reason you can’t get it to fit you could probably make a booty out of a piece of inner tube.
Sorry we (well some of us) with older vehicles had to replace a distributor cap or 2, the oem parts should suffice.
There is always rusty residue in those distributors. Usually the rotor gets changed before there is enough of it to matter.
Most of that moisture is coming up the distributor shaft out of the crankcase…
A marine lubricant, Boeshield T-9, sprayed on the metal parts, especially the centrifugal advance under the rotor, will control the corrosion…West Marine stocks this product, developed by Boeing Aircraft to control corrosion on the sea-planes they once made…It’s great stuff…
Cadillacs also had rubber distributor boots, they work good on old jeeps for 4wheeling