It all depends on the guarantee the installer gave you to cover his work + the manufacturers guarantee to cover the cylinder aswell. I fear that they will not have given you more than a couple of years in either case but it is worth enquiring just give both parties a ring and see what they say !!! But you will find it hard to prove that it has not sustained a knock or any abuse over the period of time it has been insalled. Quite frankly i am sorry to say that i think you would have more success at platting fog than getting a replacement gratis.