This is a great thread, Pat!
I just bought another of the LEGACY Light Mikado's, and I love it, but a look inside into one of their gearboxes would be incredibly helpful since Lionel has made a TON of these engines since 2011 (both Light and Heavy variants) and I know a lot of other operators who get a lot of mileage out of them, too.
It's amazing how much a little part saves the entire machine in the long run.