You are covered, no matter how old your Rimowa luggage is. At no charge.
Call Rimowa, and take it or send it to a Rimowa authorized repair store.
This happened to a collegue also arriving in North America from Europe in 2013. They had his case opened in minutes, and at no charge. He stated he was well out of his warranty, and that in hindsight, he may have altered the combination by accident himself.