On the Colt MFG website under Frequently Asked Questions it's stated that they have a 1 year warranty to the original purchaser. I believe it's been like this for a long time.
Although frustrating for anyone, fixing a loose plunger tube is second nature to a gunsmith. I wouldn't think the fix would be expensive. On the plus side would be that you would have it fixed long before Colt would have it done based on what I've read about Colt's Service Dept wait times.