Feynman examined other shuttle subsystems, and found problems elsewhere as well. His conclusion was that management’s wishful thinking about the true reliability of shuttle systems meant that, if it hadn’t been a catastrophic failure of the O-rings, something else would have failed eventually.
http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/Appendix-F.txt
IIRC, Feymann was given some info from insiders who knew about the problem, but were afraid of risking their careers over it.