I am just about %100 sure I know exactly what the problem is. The same thing happened with mine and I fixed it during NEBF.
there is a motor under the seat that has two "arms" on it. the arms have little driveshafts inside that hook into a gearbox. the gearbox is mounted to the seat base.
the back of the seat has a pivot point, and an inch or two lower has an arm that is connected with a pin. the arm basically has a threaded rod at the end that hooks into the gearbox.
what happens is over years and years of use, the grease inside the little gearboxes gets full of dust and whatnot and basically won't allow the seat back to move.
I took the gearbox / threaded rod assembly out in one piece after disconnecting the driveshafts. I believe there were two bolts, one on either side, of the gearbox and a pin with a clip that holds the rod into the seatback. ( the pin is sort of a pain to get to )
I then took a zerk fitting ( normal grease fitting ) and it was just the right size to fit into the hole that the gearbox is mounted with (same threads and everything ). the hole goes straight through into the gear.
I pumped the gearbox full of grease and then took a #2 square driver bit in a 1/4 inch socket on a 1/4 inch drive ratchet. the bit is the same size as the end of the driveshaft. If you hold the gearbox and rod steady so they don't turn, and at the same time turn the ratchet, the grease will begin to work it'* way through everything and become very very easy. at that point, re-install the assembly and then go for the other side... but ONLY do one side at a time, this way you can't mess up the seat back position.
I was going to do a complete step by step article on how to fix this ( with pics ) after NEBF, but I completly forgot
If you have any questions on that, let me know. I have a seat out of my parts car already and can go over it with you step by step if you want.