AndyMark Nanotube gearbox issue

[Taylor]

We'd been driving our robot around yesterday when we noticed a couple wheels would stop spinning intermittently. We looked closer and noticed that when we turned the wheels by hand, sometimes it would catch and we'd be unable to turn them except by force.
We're direct-driving mecanum wheels with 1/8" keys from the output shafts of the gearboxes. The wheel is perhaps a quarter inch away from the tube wall - we don't think cantilevered load is an issue.
We took the wheels off and checked the gearboxes. They were all still nicely lubed, there was no discernible wear on the gears; however, we noticed we could push-and-pull the output shaft maybe 3/32" in one gearbox, just barely in another, and the other two held fast. Especially in the gearbox with the "loose" output shaft, we could see the large gear would wobble a bit. We're thinking this wobble may be causing the seizures.
Has anybody done surgery on the nanotube gearing? We don't doubt our ability to take it apart, but putting the gears back in correctly looks to be a tall order, and one we don't want to tackle without necessity. As near as we can tell, the rings and spacers are placed where they're supposed to be - we're not missing any parts from the .stp file.
Any ideas?