I have a U4984,the same seat. The seat is pretty nice. The only thing I would change is to make it fold forward,to shed water and snow. I do not think it would be hard to find a replacement. I am curious as to why you are changing it.
The seat that came on mine I dont think is the original. It does not have arm rests like the one shown in the picture on the Montana website. I would like one with arm rests.
FYI for anyone else looking for a new tractor seat for this machine. I bought one with arms for $109.99 at TSC, not the one with the high back. The bolts on the bottom through the tracks are adjustable for the width and there are a few other bolt hole patterns to get the bolts to align for and aft. It fits great and is much better that the seat that came with the tractor.