Hi Pete
I had wondered what that plastic case is for, as despite taking the screw out I couldn't shift it for love nor money. I wondered if our friends at HL were being liberal with the glue, so with extra force and large disregard to the tank I've managed to force it off

, and lo and behold, more super glue than you could shake a stick at! Still, at least I can now put new boxes in

. For anyone who's not yet tried taking out a HL Pershing box, here are some pictures of the problem.