Since the machine was purchased last year, it is doubtful that eBay's 30 day Money Back Guarantee, Paypal's 180 day Buyer Protection, or your credit card's chargeback policy will cover you.
If the seller is an authorized dealer, which is doubtful, you can apply to the manufacturer directly. I am assuming that you purchased it New In Box and that you sent in the warranty card promptly.
Most manufacturers will not honour warranties on goods not sold by authorized dealers, since there is no papertrail certifying proper handling, or even that the seller owned the item.
Purchase another ballast.