Kondo Ongaku needing advise


Need advise from members. 

This is my Kondo ongaku amp. I bought it brand new from a US dealer in 2008. I started notice some discolouration 2-3 years ago on the copper chassis. It is getting worse. It likes kind of rusting but it is NOT on the surface. It is growing from the inside of the chassis. If you feel the surface of the chassis by hand you cannot feel it and the surface is smooth. The local dealer inspected the amp and found nothing wrong except the chassis. All other plates are in mint condition as I really take good care of it. I emailed Kondo Japan company and they asked me to ship it back to the company for repair/ replacement. I live in Asia and, even do, the company quoted me USD 6500 for replace of that chassis. Anyone has a better idea of what it is and how to treat? It’s a bit too expensive to replace one chassis at the cost of USD 6500.


nicksun
Clean with brasso and apply a clear lacquer. It will take time but not 6500 usd of your time. I did this to an old Sherwood and it turned out beautifully. That’s a great piece and worth the elbow grease. 
Also you can clean with Silvo, it's apparently finer than Brasso, maybe finish with Silvo, just a thought. 
If you clean it with Brasso Silvo or other stuff the best it is to finish it with Cape Cod polisher and you can not apply poly or other sealer you have to clean it with gunk or alcool 90% to remove all grease and product thing before put poly or métal lacquer if not it will peel of ....I am french excuse my English 

Solid copper… it is a piece of art, both sonically and construction.

my 1990 is in perfect condition, it gets polished with a copper polisher and protector.

Get it repaired, $6500 maintenance for a $100k amp is nothing.