there are wires #6 and #8 on the control card that control fwd/rev signals, (the same row of 6 terminals/wires edward is speaking of), test there for directional output signal to the directional contactors. (since this seems to be intermittant you may not see it all the time)
You also need to insure the seat switch is working correctly and does not have any break in signal, check the wires and even the switch in the seat itself and make sure it is not loosing connection.

And lastly the directional contactors are still suspect, they are known to cause these exact symptoms, i've seen them where they look perfectly normal but the insulators and other moving parts would be worn in such a way that they would not allow the contacts to connect correctly causing incomplete connection in the drive circuit keeping the motor from running.