I've been told that leather is treated with urea which makes it smell
like an attractive place to pee; the fact that your cat's pee has never
been fully cleaned up just emphasizes the giant neon sign reading, "PEE
HERE!"

I think you might have to get a leather cleaning expert to clean the
chair. But after that it might be hard to break his peeing habit without
separating him from the chair: put it in a room with a closed door.

In male cats however, you always have to consider that they might have a
urinary problem that is making peeing in the box uncomfortable and
causing them to have frequent and strong urges to go; at which point
they might let loose right on the nice soft comfortable surface they're
nearest to. If you suspect any kind of urinary problem, take a trip to
the vet specifically to check out this concern (an ordinary wellness
exam doesn't usually include a urinalysis which is necessary to see if
anything's unusual).

-Alison in OH

Chris,

   You may want to try Feliway. It stopped my cats from urinating on my
leather couches and other areas around my house. I'll post the link below.

http://www.feliway.com/