Don't use hot glue. Use gasket maker. Read my tutorial on GBB mags and z0ng's on WE mags.
Most common on the original WE mags is a main seal failure. Causes vary from drying up, poorly assembled and breaking the seal from a fall/drop. Then it's a toss up between the fill and flow valves leaking but I they are easy fixes. I haven't tried the new ones but their design is more like a GBB pistol which is less prone to failure.