Hmmm. Not entirely sure that this is the case.
I enquired with Thomann about a stage piano recently (okay, okay, I know it's the wrong forum) that I was looking to buy privately from someone local to me, but had originally been sold by them. It was about 6 months old.
They said that they will continue to honour the warranty, but instead of it being a 3 year warranty, it drops down. I can't recall if it dropped to a year from when I bought it, or 2 years from the original sale, but the point was there was still a warranty. This was Thomann, but it may be the case with other sellers.
It also applies in many other cases. Car warranties are transferable if the car is sold.
I'd say find out where it was originally bought and also contact the manufacturer. If it was a manufacturing defect you should be protected. I would also point out to the manufacturer that this wasn't something that 'broke' it was wrong from the day it was built.
If worse comes to worse, then you could threaten the manufacturer with taking them to the small claims court, but try and exhaust the other possibilities first.