I don't remember now, it was 7-8 years ago but it was a common, well-known supplier of the sleeved MCs. The original sleeved cylinder (on the bike when I bought it) began leaking and when I removed it there were some markings on it that I searched and then found the supplier. I sent him an email, he confirmed it was one of his and gave me the address where to ship it for resleeving, which I did. The second time it failed (several years later) was when it went from normal brake to no brake between stops. There is no feeling quite like pulling the brake lever and having NOTHING happen!
But we all do what we are comfortable doing; if other riders here are comfortable with the sleeved MC, that's great. But the experience made me totally gun-shy toward them.
I suppose it's no different than any of the "arguments" here - what oil to use, safety wire or loctite, what ignition system, Amals or single Mikunis, etc... Compared to brake reliability, though, those other items are pretty much insignificant from a "saving your A%$" standpoint!