Corrosion
Wherever there is an electrical connection between the cones and between antenna elements there is the possibility of corrosion. In the feedcone that I just received there is corrosion in the element sockets. These need to be cleaned with a small arms cleaning brush and I need to find an anticorrosion compound at my local hardware store.
My antenna was put up without any preventive measures and after a couple of months the antenna elements had locked to each other. Large pliers would not undue the joints. The cause was the copper oxidizing. Compare a polished and corroded MS-117A end. You can see that both Silicon Grease and COAX-SEAL are needed at every joint. The reason for adding the COAX-SEAL is that water is the universal solvent. Given time and weather I am concerned that the Silicon Grease is not enough.