I have a 10" wingnut adjustable shower arm in one bathroom, and it has sprung leaks from both joints. I'm guessing it's a couple years old. One of the metal cup-shaped escutchon washers has a small divot at the edge (this joint leaks the worst). The shower head is just a nozzle - nothing heavy. It leaks no matter how hard the wingnuts are tightened.
A little research revealed that this design (AquaFlux & others) is prone to leaks after a year or so. Lowe's sells a rebuild kit, but I'm wondering if the design is flawed, and ,no matter what brand you get, you're going to get leaks after a year.
PErhaps you could replace the o-rings in the joint (if it has o-rings)? Might get some plumber's silicone grease and smear some on the mating surface when you reinstall. Might last longer. Cheaper than a new arm I'd bet and especially if it works.