I think that GB members probably have come across certain doctrines they question, but this being "Gods only organization" and because thesee teachings have been so ingrained into the religion, any doubts could be brushed off. And let's face it, being a GB member is no cake, they're probably off doing a lot of organizational work, keeping their minds on other things, planning for future structure of the religion, traveling, and such. They probably don't even take the time to examine things closely. It's like what Ray Franz said, many hardly had time to read the Bible or have a close examination of it when receiving questions. Not to have them off the hook for their actions, they've heard probaby heard opposing points but choose to ignore it or not even deal with It, even if it's reasonable like on the 1914 subject back in the late 70's.
It would be cool to have an ex-GB member tell their story like Ray Franz did, and updated version of today. But it's unlikely there will be one anytime soon. Part of what got Ray Franz to question was his work on Aid to the Bible understanding book and examining things scripturally rather than resort to Watchtower publications.