I haven't checked my warranty book.......but in only five months..... I would take it back whether it was or not. At least you can take the seat off to return it.
kubota L 3540 hsdc,B 2320 hsdc & lots of other stuff!
Take back the old seat,if the dealer will credit you for the old seat, upgrade now. Unless kubota has changed things, that seat on the 75 series is really bad! I had that seat for six seasons, my back is still recovering.