Before you get too excited, check as some state regulations will over ride other legislaitions.
I did say should.
As for the hydros, you have 2 one left & 1 right and only the replacement unit will carry the warranty.
The other crunch is how carries the can, the tranny manufacturer or the mower manufacturer or the service agent.
Down here, where most of our consummer laws are directly copied from California legislation, I the repairer have to warrant any & every part that I replace is of the same or equivalent quality as the part I am replacing.
SO if the trany had 12 months when new & I replace one that is 20 year old, it still carries 12 month warranty from the day I installed it.
It gets even worse down here because if I send a mower out with any defective part on it and it fails , I am liable to repair it regardless of weather it was the reason for the repair or not.
This was done at the behest of the vehicle importers & manufacturers to discourage the repair of old vehicles.
The length of the mandatory warranty depends upon a ratio of the repair price to the original RRP.