Thanks, everyone. As eaglefreak said, I too had heard that the effectiveness of all forms of lock washers isn’t as good as we've been led to believe. Based on experience, though I still think that a good-quality hardened steel (not cheap common steel) split washer can provide some insurance to a bolt loosening. I also suspect that split lock washers could decrease the accuracy of critical torque readings, which I don’t know how to compensate for. Fresh blue Loctite is pretty good stuff, and the red Loctite is the really serious stuff, i.e., much more permanent. Since one of these joints has already come loose, I’ll try to do things as correctly as possible. That means getting an M10 x 15 tap to clear the old LocTite from the flange threads, cleaning all grease and oil of off everything, using FRESH blue Loctite (I understand that Loctite had an open shelf life of about one year), torquing everything correctly, and giving the flange bolts a look at every oil change. I’ve got to sleep on whether to use flat or split lockwashers; I’m still 50-50 on which I’ll use, but I’m probably leaning towards some good hardened steel split washers.
Thanks again.