I've got a brass mount installed on my car which has a 3/8-24 socket. All the antennas I'm looking at seem to have stainless steel connectors. Is packing the connection between antenna and mount with dielectric grease enough to keep out water and crud and prevent corrosion, or is there something else I should do?
Not sure about how that would exactly look on your car and if it makes sense in your case, but I have successfully used self sealing tape to proof antenna connectors outside (as I got the tipp from other hams). Just be sure to apply enough force for the tape to seal but not too much, so the connector/mount/cable doesn't get damaged.
Brass and stainless steel don't corrode hardly at all so you don't have to do anything in this instance.
I would just leave as is and then every year or so clean out the accumulated rubbish with water and soap.
As does Stefan, i also normally use electrical tape to seal antenna connections on a car if required and replace every so often when the tape starts to get affected by the sun and weather.