Sam's for the 11 can be found here:
http://earlytelevision.org/pdf/rca_ctc11_sams_550_2.pdf
I don't see a M1 on it, but then again I did not take much time to carefully look...
If socket pins, that are shown on the schematic as grounded, measure over an ohm to chassis, then either the ground path is bad, your meter has a problem, or the connection points are dirty. Suspect board to chassis ground connections, traces, and socket in that order.