Hey DBK,
That shaft is PRESSED IN, at factory, steel shaft pressed into aluminum housing, at a set degree, to keep camera LEVEL! The only way I found to fix this, is to put it together, level, then mark shaft and aluminum ( to keep aligned )
( please review pitch board/shaft alignment on YouTube to keep flat part of shaft aligned correctly with pitch or roll boards )( CLEAN AREA REALLY GOOD ), then mix up a bit of ( 2 part epoxy ( good stuff )), epoxy the hole from the inside ( not too much just a dab ) place gimbal together ( shaft into hole ), put gimbal clamp on to keep gimbal secure, while epoxy dries! This should fix your issue! ( take your time to try to get as level as you can ) I've done a few, they don't always turn out level, but if not should be very close, I've had to tear them back apart and retry to get it right.
Or
Option 2
Buy a used arm on ebay ( around $20 ) and just replace the bad ( wallowed out ) arm all together!
Usually come with motor and all!
( but that is a LOT less fun! Lol )
Hope this helps
J Dot
