Loctite is the way to go on metal geared servos when using metal arms. Even though you apply the loctite to the threaded hole only some vapor will get to the plastic arm and you might have an issue. The first thing to do though is to get rid of the crappy screw that comes with the servos and order up some 2.6mm socket head screws. With the better screws you can get the screw tighter and then if using metal arms apply loctite, if using plastic arms then stake the screw with RTV.