The flat spot needs to be just big enough to give something for the screw to work on. Also, blue lock-tite seems to be strong enough from what I've seen while making it relatively easy to remove.
I agree, only use blue lock-tite... the red stuff will ruin your live!
I would also get that Lehner front bell cover as well, that should fix your problem.
“The modern astrophysical concept that ascribes the sun’s energy to thermonuclear reactions deep in the solar interior is contradicted by nearly every observable aspect of the sun.” —Ralph E. Juergens