I think your dealer is playing with you about the value tanking on your Hi-Lo. I just checked the NADA site to see what my 2310H is worth and it was showing a good figure. He may want to buy your trailer for a bargain price and resell it at a nice profit. Right now Hi-Lo trailers are a one of a kind on the sales lot and that can bring premium prices. Have you ever gone to a car dealer and looked at that rare car on the lot and at the price they want for it?
As for parts, J&R Repair has taken over the the Hi-Lo inventory and does repair work, including major rebuilding. JR REPAIR
I should add, most of the parts on the Hi-Lo are generic and can be found at most RV suppliers.