I have an Electrolux (Frigidaire) stacked washer/dryer combo that is not agitating. The control circuity, lid latch, motor, and belt all seem to work. It fills, drains, spins, and with the lid open at the agitate cycle, and the switch manually engaged, the motor spins. Grasping at straws, I pulled the agitator itself off, and the "drive block" (spline gear) which is lose enough to turn does not turn.

I note that the transmission itself is stationary while the washer is in agitate cycle, but is free to and actually spins itself while in the spin/drain cycle.

It isn't clear at all how the transmission is signaled to engage the drive block, vs spinning the tub.

Is there any more reasonable steps I can take to diagnose and repair? 

For clarity, my machine is an Electrolux mex731cfs1