Having a dealer flip you to a 3rd party like an axle, frame or other items is standard practice in the industry. BTDT. Not right as far as I'm concerned since you have a purchase contract with the dealer.
Even if a dealer agreed to repair something, don't count on them knowing what to do or how to do it properly. BTDT too many times in the last few years.
Don't even trust what a dealer tells you. For ex., if they come back with a "it's within spec." don't believe them. And if a dealer is supposed to have done a bearing repack, don't trust them to have actually done it (another BTDT).
The standard plastic bushing in the springs/equalizers are carp. Ours were totally shot in just the 2K+ mile trip from Indiana to our dealer. Now have Dexter equalizers and wet bolts.
Be glad that's all that went wrong. Sometimes frames don't last a year or even a month... We have a story to tell on frames but can't. 'Nuf said.
If you don't know what to look for in terms of the root cause, I would take the TT to a reputable and experienced frame and axle shop. If the source of the issue is found, get a report c/w photos and send it to the dealer, Nash and the axle manufacturer.