Unless parts are unobtainable, anything can be repaired. It's just up to you whether it is worth it to do so. If it was me, I wouldn't hesitate. You would spend approximately the same for a used REF 5SE vs getting this one repaired.
I would bite the bullet (never understood what that means) and get it repaired. But, that's me.
As for the cat, well, you have received lots of "advice" from cat lovers and non cat lovers alike.
Take your choice. However, this is a part of the family and an animal. They, like children are trainable and will let you know when they are unhappy. I would never allow a cat anywhere near my audio equipment. But, that's me. This is what happens when you have pets that aren't trained, or want attention. Well, it got your attention.
My question to you is, what are you going to do about cat so this can't happen again? no joke. The cat (like children) must learn that it isn't okay to do this. So, what will you do? If you do nothing, then the cat (like children) will run your house.
If the urine problem was that severe, which I doubt, I would get a new stuffed board and you are done. First, since this is what I do also, I would inspect the board and diagnose the problem and try to fix it before replacing the board.
I'm not a cat person. But, I've lived with them and know they have attitudes and issues like any other animal. But, if you don't teach this cat to never do this again, then guess what? it will.
So, here are your options.
1. Sell the pre-amp as-is with full disclosure.
2. Buy a used REF 5SE or better yet, just get a used REF 6, or
3. Keep the pre-amp as a paper weight and go to 2, or
4. keep the pre-amp and get it repaired.
5. Train that cat!!!!!!!! Because if this happens again or something similar, then it really is your fault.
Anything is repairable.
enjoy