If it weren't a valuable item, it wouldn't have made it to the car.
The term "Valuable" is subjective
But if so, refinishing the stock will really diminish the "value" of that firearm
Plus, the gun just is not going to look right.....He is would have a freshly refinished stock on an abused/neglected firearm?
What does the metal and the rest of the gun look like? ( ...allowing a cat to piss on it is neglect)
Your friend will need to put the Correct stock on it if he wants to maintain "value"
I might think so. Why would anyone put a wretched smelling cat piss soaked gun (or anything) into their car?
He can't put any ole stock on it, nor a repop if he expects it to stay "valuable" or retain it's value.
The "Correct" stock is a Big discussion for another day and time.
There's a lot with old firearms and Correctness is a BIG thing
Been collecting for decades....
About the cat piss,
Once upon a time a bunch of milsurp rifle parts were brought in from Turkey where the Turks (reportedly) cured their leather slings with urine!
The smell was so obnoxious and Ghastly that the slings were Total throwaways!