My rear right tire is slowly losing air. I've put air into this tire 3 times in the last 3 weeks. It's needs to be inflated to 30psi. I filled it to 35 psi every time. Now, for the fourth time, it needs air again. What are my options? I'm assuming it has a small pin-hole somewhere. Is this something that a dealership can fix? How much does this generally cost..what will they do?