I just went throught a similar problem with mine recently. Most likely, it will be the seat control switch. In my case, it was the seat control memory. I ended up buying a used seat. Also check the tracks for blockage. If everything else fails, you have to take the seat out (not hard if you have access to the 4 bolts) and test the motor. I think there is a total of 5...3 for the seat bottom and 2 for the back/headrest...but, you only need to test one of them.
I do not think it is the motor since it is moving forward...

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J.H.
'86 300E