The first thing to say is that a manufacturer's warranty only covers faults in manufacture - it will not be any good as far as wear and tear is concerned. The seller may have told you the card was 12 months old, but do you have any means of verifying that?
In general terms a second-hand purchase is protected in the same way as that of a new product, provided you buy from a retailer. If you buy from a private individual however, the regulations are different - the transaction is classed as a private sale, and the goods you buy must only be correctly described, and be the legal property of the seller. If you were told the card was 12 months old, that's all it has to be, there's no assumption of it being fit for purpose - that is for you to determine. The old adage of caveat emptor applies.
In your own words, the card "was in great working order and worked fine in my PC for five months or so." You have no recourse to the seller, and you obviously acknowledge that fact.
The manufacturer has no contract with you (or with the first owner), so there's no liability in law there - the manufacturer's warranty is in addition to your legal rights, so you'll be in uncharted waters; you may be lucky and find that the maker will help out, but I wouldn't bank on it. You have nothing to lose by trying, so why not give it a go?