Pfunk, I hear ya man. My wifes got the exact same model. Exactly. He's 15 goin on 16 and hangin in there. She rescued him when he was a we mudball and loves him more than she does me I think.
He started getting skinny as hell and eating like a horse about 2 years ago. I told her to take him to the vet, but she piddled around thinking it was because we moved or something. Eventually I told her if she doesn't do something soon he will DIE! That got her.
She took him to a local country/horse vet who said, "humm, looks like he's getting old". She brought him back home and told me the same thing. I said Bah! Take him back to his old vets, they know him and he didn't look like this 6 months ago.
I'm not saying she didn't love the guy, but I think she was trying to prepare herself for his demise. Finally I prevailed and she took him back to the old vets place. They diagnosed him with the same thing(hyper-thyroid) plus complications. She started shoving those pills down his throat and he got a bit better, but started tearing his face and ears to shreads. She took him back. He lowered the dosage. He scratched. She took him back. It turns out that he is allergic to the only known medication for his condition.
The vet came up with a novel idea and got in contact with a pharmacist freind of his and they concocted this cream stuff with the medication mixed in and told her to rub so many millimeters of this stuff in his ears every day. After a few adjustments, they got it right and the Smokemiester is still alive and kickin. No more scratchin, but still eats like a horse. He puts back on about a half a pound every 6 months.
Dam cat looks like Bill the Cats 3rd cousin, but he's still kickin! I will hate it when he goes, my wife will go bannanas! Of course, I'll miss him also, but not his pissin in my shower!