ecoli
I wanna be Dave
Go aluminum. The Traxxas big bore aluminum shock caps are a direct fit (Traxxas part #2667). Wrap the threads with teflon tape and screw on the shock caps. You'll have to use fuel tubing instead of the metal ball joint, but this is a quick, easy fix that will end your shock cap popping problems (at least it always has on any other shocks I've done this to!).
Chris
Chris