Okay, I was messing around with HD Anakin last night, and decided to remove both magnets in the arms and use a paper clip to make it sturdier, yet still removable. I removed the magnet from the stump first, using my knife, but I dropped it.
Well, when I found it again (after searching around my floor) I noticed one end had some specs of brown where I had shaved off the paint, and one end had a spec of blue. When I moved the magnet closer to the severed portion of the arm, the blue end instantly jumped to it! So I flipped the magnet so the blue end was facing out and put the magnet back in the stump, and the rest of the arm like even tighter than Zam's arm! So I glued the magnet back in and left it, and now the lower half doesn't swivel or fall off so easily.
It's an easy procedure. Other Ani's may not have the blue spec of paint like mine did, so mark the original end first before removing. Trust me, it's much better.