Aha! Under my close scrutiny... there looks to be the sleeves and elbows consist of a series of washers and a spring sandwich, clamped firmly together in between a long screw and a hexagonal nut. This is THE MOST AWESOME JOINT CONSTRUCTION I HAVE EVER SEEN IN ANY PGs ARM!!!
This bodes well for the rest of the kit's mechanical design. (though I'd have dearly loved the 2 condenser windows to have had light up gimmicks... you can't have everything.)
Modified image originally from the official Bandai site here http://tinyurl.com/n5tekc