I thinks its the split frame. The gears are the leftside which are flush with the drivers.The siderods and the piece that holds the eccentrics in place is meta;.

I have an older model of Bachmann's 0-6-0 which in those days had square tender, not this slope back one. It came in Bachmann's yellow and black case. The main gear between the worm and middle driver gear is stripped! Any ideas if the newer model 0-6-0 gear will work?