why are you paying "a few thousand" to install it?
don't take this the wrong way but that seems terribly high to me... hell, for "a few thousand" i'll come up and do it myself!
to answer your question, MOST used items, or hell, even new items themselves are covered for instances like this but DO NOT include labor...
if i install a sliding door in your house, whether new or used, and the track breaks... you get a replacement door, would you expect me to come out and install another one for nothing?
Did I buy the sliding door from you? Or did I have you install one, that I bought from someone else? Just askin
But I'd much rather have french doors. Can you install those?