My second conclusion was that citations are like a game of telephone and every time someone cites something, it changes slightly, so don't trust anything until you get to a primary source, and maybe don't even trust that. (This second conclusion applies in general, not just to Murray.)

This part is definitely true. It has also been my experience -- but more so within academic areas with sloppy "researchers" and political problems. Linguistics is pretty good, gender "research" is awful. Intelligence research is pretty damn good, social "science" and psychology (outside of psychometrics) is awful. Economics is awful, apart from the basic ideas of competition, capitalism, and low taxes. Keynesianism is largely a fraud.

My conclusion was that his book is junk.

This is unlikely to be true.