I met all of them that were around during the 90's. I'm related to one appointed since then. Most of my contact was while in Bethel and several on this forum have had the same experience.
As for "defects" they freely admit to being counciled on things like envy, pride, humilty, etc. As for sin they state that all men are born into sin, that includes the GB. I would be suprised if any actively engaged in "major" sins, but not because of any special strength. Most had been in the service for decades before they were appointed. If they were prone to something like, for example, adultery its unlikely that they could hide it for that long. But then again how hard is it for a 70yr old man to avoid adultry.
Three were were removed\resigned around 1980. Two for probable homosexualty, another for apostasy.
Some also make the case that they are all guilty of apostasy. But you have to figure that out for yourself.