Unfortunately pet urine odors are VERY difficult to impossible to eliminate. You may need to buy a new seat cover and foam base to start nice and fresh. I don't see this as a wash and dry and all is well ending. Hope I'm wrong.
For that thought of dollar cost it might be more cost effective to replace the cover and foam and he'd be guarenteed that there wouldn't be a smell.I do not disagree, however a pro detailer should be able to handle it if he is told that it is urine.
He might also know how to disassemble seat for more cleaning.
I am not talking a $20 fix, it's gonna cost some $$.
That could work but MUST soak in as far as the pee did to neutralize it, so I think the seat needs to be taken apart. Now if it's disassembled that would be the time to replace it.white vinegar mixed with a little water. then use a foam upholstery cleaner to clean the whole seat.