Okay, first Sean you need this new part. I don't know if this would work with the LionChief engines, but @gunrunnerjohn made a post elsewhere on this forum about using the plastic snap closers from bread bags as a snap in spacer to help gears align better.
I had one engine with one axle that wasn't engaging the gear as good as it could. So I tried John's idea, so I took one of those bread bag closers, cut it down in size just a little bit, popped it in on the opposite side of the geared wheel on the engine, and it made a big improvement.
Granted, this doesn't excuse poor design engineering. And I'm talking about improving an engine I paid $35.00 for, not $250-$300. But John's idea certainly helped in my case, and he has had experience with train repairs, so maybe (?) he would know.
This here is one of the reasons I stick with "tried and tried" instead of "new and improved," which might not always necessarily add up to "improved" as much as "new."