Hello 22 Racer: I have put many antennas up, and taken a few down and apart, neven seen any need for a die-electric grease, as 30 year old aluminum antennas come apart by just removing the screw or hose clamp.
No corrosion or aluminum dis-coloring ever seen.
I know guys that are real close to the salt air like near or on the ocean will use electrical black tape to seal the aluminum connections after the antenna is assemblied. But other wise its aluminum against aluminum not a big deal.
Most antennas used in the CB and Ham Bands use a SO-239 connector, so that the PL-259 soldered onto the Coax will mate, and make connection. These connectors are not water tight, and need Silicon, or RTV, or shrink sleeving, or again a good black tape sealing them from the weather. Keeping the water, mud, blood, and beer outta of the Coax.
Some antennas come with a rubber boot that fits over the coax, so that when the connection is made the rubber boot slips over the coax, but still needs black tape or Silicon/RTV to properly be sealed.
Water in the coax can be detected by occessionally measuring the bandwidth of the antenna, measuring the SWR on CH 1 and CH 40, if this measurment shows a increase in bandwidth then its possible that water is gettig into the coax, which causes the coax to have more loss, which will be indicated by a better SWR Bandwidth between CH 1 and 40. As the coax has more loss the SWR Bandwidth will get better, but your rec and transmit signal will be less.
Jay in the Mojave