I would simply note that if "this stuff worked great for 25 years" then you have indeed gotten the use out of it. If only everything else worked as long in our disposable civilization. Amortization of price versus the number of years you got out of them isn’t bad.
Sell them "as is" on eBay or part them out if you want to go to that much trouble to get a few extra dollars.
It is sad that BAT won’t repair it and give at least a 90-day warranty on that repair. With it being their design, they should be able to troubleshoot it and fix it. That was always the great thing about tube gear using discrete components instead of solid-state gear using integrated circuits.
There's a lady electronics tech on YouTube, goes by Skunkie Works, that often does videos and teardowns of Chinese made tube gear and others, and then she sees what, if anything could be better and upgraded for better sound and/or safety.
She did a great series on the Willsenton R8 and R300. It looks like regarding the R8, the company took some of her suggestions and incorporated them.
She might be interested (for a price) in seeing if she could repair it - and likely do a series of videos on why, how, and what she did. Just an idea better than dropping it off at Staples.
Good luck.