I guess we've been very lucky then. I think poor engine design, like in some Toyota applications, and neglect are the biggest problems with sludge. Running an oil for 50,000 miles, is insane, and stupid, especially in an engine like some of the Toyota engines that are prone to problems by design.
Would Synlube back up a Toyota sludge prone engine that failed with it in the sump for 50,000 miles? LOL We were questioning Amsoil, I don't recall anyone asking about Synlube.