My seat did the same thing after my friend ripped off the adjuster knob getting out of the back. I tried to put it back together again, but the knob wont stay in. You can try pushing the knobs together from both sides and see if that makes it work, if so then at some point the knob has been dislocated from the splined rod.

Mine was under warranty so I had the seat back replaced, seems to be working fine now.

As for warranties, do a google search. I found several sites of companies that offered extended warranties when I was researching my purchase.