first i would check the bolts that hold it down on the floor body if those are tight the check that any metal around those bolt holes is broke or cracked (meaning that you got a bolt and the area of metal it screws into all comeing up as the seat moves ) .
if none of those are the culprit then check under the seat it's self to see if the motor ( i'm assuming the eb's had motor seats) houseing is loose and see if the drive cable shafts that lead to it move .
also you may just have a broken seat frame below, try to take the seat out and flip it over to get a better look at all the control cables and support metal that is attached to the frame.
hope this help