Do the sport seats in the '90 model year have a zipper up the back? You really need to remove the entire seat to properly (and easily!) get at the seat backs.
If there is a zipper, remove the seat, unzip the zipper, and un-snap the bottom of the seat back leather from the plastic channel into which it "locks." When you get to the unzipping part you will see what I mean.
Have fun reassembling!
