A friend of mine who fixes G scale locomotives asked me to mention that he has found that Bachmann is incorrectly listing the 2-truck Shay coupler mount, part number G821X-00B03. If you order that part, Bachmann ships the Climax coupler mount instead, which does not fit on the Shay. He has contacted Bachmann several times about it, but they have not corrected the problem.
Apparently, that part often breaks, but no replacement is available.