Several here have done the cat pickling routine, I think it has been recommended by Woodstock for years, and Jotul before them. I’ve never seen BKVP actually recommend it, but I’ll let him speak for himself, there. He is here nearly daily.
Most here seem to get a mild extension on the life of their cat, when doing this. Maybe another few thousand hours, it would seem.
@Highbeam is our most recent expert, on this old subject.
As to why you’re seeing a reduction in performance after 2.5 seasons, that has to do more with statistics than anything else. The 10 year warranty is based on most (90%+?) of their customers using their stove 1000 - 1500 hours per year, against the typical < 15,000 hour lifetime of a cumbustor. That small fraction of customers who burn their stoves 24/7, which also happens to be nearly the same population who spends their free time on a hearth forum, will run up that 15,000 hour lifetime much more quickly. Sometimes as quickly as 2.5 years, and BK is apparently fine with eating that relatively small cost for this relatively small population, to continue marketing a 10 year warranty.