Galvanic corrosion will occur where aluminum (valve) and steel (air tube) meet, in the presence of water condensed out of the air.
Scott reports CorrosionX is very effective.https://www.gatewaytoairguns.org/GTA/index.php?topic=140812Something like silicone would at least be better than bare metal on metal...anything that is insoluble to the water that promotes the galvanic reaction, and viscous enough to stay in place over time. I always use a foam pad to apply a thin film of silicone oil to the pressurized part of air tubes when reassembling a gun, and have yet to experience this sort of corrosion. Though I have found it from time to time when working on others’ guns.