Sometimes it's easier to access the individual motor connectors from the rear. Along the back edge of the seat's memory controller the individual motor connectors are lined up, you can unplug each them until you find tye one that controls the forward/backward motor and with a couple of leads with female connectors apply 12 volts and thereby bypass the memory controller which may be the problem as it appears that there is some intermitent electric current being sent to that motor.

The four pole plug has two small connections and two larger connections, the larger ones are the drive voltage connections the smaller ones are the feedback position rheostat connections.