I don't agree with spreading heresy, but you are simply wrong about him saying "mater si, magistra no". See the link I gave for the story on that: It's a quote from Wills, not Buckley, and it isn't referring to Buckley but to Frank Meyer. The two quotes I gave you from Buckley on the encyclical are written 3-4 months after it was published - that's awfully fast for a memory problem.
I'll bet I have a copy of that kicking around. I'll check.