I have never heard of servicing calipers for any other reason than to clean and lube the guide pins when brake pads are replaced. If they needed to be serviced every 7,500 mile that would be represented in the owner's manual. I have worked on these cars. The only caliper maintenance that needs to be done is when brake pads are replaced. I don't think the dealer was being truthful and he certainly didn't take the time to explain the problem and what needed to be done.
Lack of communication causes a lot of problems.
Even though we normally recommend a call to the automaker's Customer Service line to ask about these things, a phone call might not have helped as they often side with the dealer. The Byrnes Family Dear Byrnes Family, We recommend that you always stick strictly to the manufacturer-recommended additives. Short cuts can, at times lead to much bigger problems. But putting camphor balls in your gas tank sounds like a good way to clog up your system.