That sucks and I know how frustrating situations like this are.
I am very surprised at G-K, though. Years ago, I bought a new 400RB head that was a lemon right out of the box. I bought it online from Bass Central, and this was ages ago, but thisthis shipped me another new 400RB immediately and paid for the shipping to send the lemon I bought back to them.
G-K also did a cooling fan upgrade on my old 2001RB head on their dime, and the turnaround was surprisingly quick.
I sure hope G-K's once stellar Customer Service hasn't gone south, your post leads me to think it may have.
If possible, call or email G-K again and ask if you can take this issue up the chain of command and see if that helps. If you bought it new from an Authorized Dealer, and these problems started within your warranty, I'd think you should be covered.