Until "back and forths with the customer until they create enough pressure on our higher ups so that they have to order him to change that code", I was going to

Until "back and forths with the customer until they create enough pressure on our higher ups so that they have to order him to change that code", I was going to suggest polite ways of asking your manager to get involved. After that - sounds like your (and/or his) manager are too weak/ineffective to fix the obvious problem. And more of the same, up the chain. How long have you been there, and what might other coworkers think? I'd probably be polishing my resume - on the theory that low-functioning orgs can go away fairly quickly. And that what I didn't know about the politics behind that mess could still hurt me.