I've had my XL for almost 3 years, and I'm looking at my warranty. 20 years on ceramic parts, 5 years on non-ceramic parts, 30 days on the gauge and gaskets.
Warranty is non-transferrable.
If I were looking at a used one, I'd look very closely at the top, bottom, insert (firebox) and the base that sits inside the firebox for cracks. The exterior glazing will probably have checkering all over, that's normal.
If the seal needs replacing that's not really a deal-breaker, they can be had on Amazon (various materials) and there are numerous how-to videos on YouTube.