Instead of silicone you should try some dum-dum I know its a stupid name but its like the sealing stuff in rolls that they use for your winsheild, or the real name is rope caulk black in color put some on the end of the shaft and make sure there is enough to hold the cap down, it say's pliable in all weather but may ooze out in real hot weather, so if you ever have to remove them you can without any trouble or screwing them all up, this is what I am going to use [ and KrzyFast why not call the dealer and order them and see if they will mail them to you free of charge it can't hurt to ask them]