Could you go from it with the angle of - I thought you & I communicated so well that you of all people would be able to clear up a few things for me. It's only a discussion, I'm not 'attacking' anything, only asking a few questions. For instance, I was always taught xxxx, but looking into it closer I have found yyyyyy, and yyyyyy and yyyyy. What do you think about that? (if you include wt quotes it may cut down on their cut & paste)
I almost ditto this response from Carla, but others make a good point. You don't want this person seeing you as an attack dog, tearing down, sent by Satan. Perhaps you could say "You and I communicate so well, I really want your help." then back off a bit. Just mention things here and there, don't try to always appear overbearing. Then the communication line will stay up.