Here's two pics I took showing the hand (sitting on the wrist) and off (Sorry for the poor image quality):
I don't know alot about modelling or toy construction but it looks like the peg is just too small to keep the hand on. The peg doesn't look worn or damaged in anyway. Maybe the worn looking lip on the hand itself is what's supposed to keep the hand on?
Someone told me this morning that Robotech.com's store is agreeing to replace broken Alpha MPC's.
I would suggest if yours came broken or broke right out of the box that you visit or contact by phone or email the store you purchased from and politely ask for a replacement.
In fact Armo just posted about it at RT.com:
ArmoDiver
Rank: Private
Subject: If you've got a defective one...
Posted On: August 20, 2004 - 1:27:23 PM
Like mine, which broke almost as soon as I opened it, or just the victim of plain shoddy workmanship.
E-mail their customer service. They'll replace the toy.
If enough of us do this, maybe they'll do some serious checking into their quality control. (Or apperant lack thereof)