I'm in the process, and I do mean process, of resurrecting my '85 S that's been sitting for 4 yrs in a humid environment, and darn it if the rear seat backs are frozen solid.

Solid to the point that the plastic release knob broke upon  attempting.. release.
I've doused everything liberally in WD40, but wondering if anyone's been  there already & found a trick.
I suppose I should retreat to the service volumes around now, but given the more imposing tasks that lay before me, I'm a little over it.

I've been through http://www.nichols.nu  , but all steps seem to start with 'move seatbacks forward' Yes, if only.

About to join Dan's 928-Haters Club,

-Chris
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As has been said elsewhere, WD40 evaporates. Try something a  mechanic told me; use ATF. High detergent content, good penetrant qualities, and it doesn't evaporate. YMMV....
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Chris,

My experience with WD 40 is more hype than results. I have never seen it free any rusted part.

You might want to get some Kano or at least some Liquid Wrench to soak the hinge on the seat. The plastic handle on the seat is a common thing to break. It is connected to a lever that is connected to a long rod going from the top of the seat to the hinge. The rod operated a locking lever over the top of a substantial round pin. Since every thing on the hinge is stronger than the operating mechanism the upper parts will break log before the latch comes loose.

The place to put the penetrating oil is on the seat hinge on the outside of the seat. The inner hinge is just simple pin going into a plastic bushing through the console. On the older cars you have to remove the seat backs before the console. On the newer cars (S4 and up) the console comes out first as there is a second inner hinge bolted to the frame of the car.

Now for some tricks. It is easier to free up the hinge when the seat is out of the car. I use two tools. The bolts holding the hinge to the car are
cap bolts so you will need an Allen or Hex wrench. I have a long T-Handle hex wrench with a ball on the end to allow it to operate at an angle. I also have a hex wrench as part of a 3/8 inch drive socket. Both are helpful.

The carpet on the back of the seat has a couple of screws going into the car. These need to be removed first. Once removed you will see the hinge. If these seat will not move down then the lower cushion has to come out first. These are glued in. I use a putty knife on these to separate the seat from the insulation. Just go slow and the seat comes out. Who ever  thought of gluing the seat bottoms in should be shot.

Once the seat bottom is removed you should be able to get access to the bottom cap bolt. It should come out with the ratchet and an extension.
Hold on I may be wrong here. It might be the top cap bolt you have access to when the carpet is pulled back. I do not remember exactly since it was a while since I encountered this problem. Either way you should have access to one of the two bolts. Once one is out then the seat will pivot enough to give you access to the other cap bolt. The entire thing is not so easy but it can be done.

As and alternative if you have a seat out or can find someone with this out, look at the hinge. You will see if you use a screw drive just so the latch will pop lose and the seat will tilt flat. I found the seat has two lock point - one in the upright position and one in the folded down position.
Once the seat is flat, if you release the latch the seat will fold down a little more giving more access to the two cap bolts.

Sounds like fun.

Dan the Pod Guy
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You can bypass the plastic release knob by going directly to the metal latch located on the side of the seat back closest to the car body.
You can move it with your finger with some effort.

My seat, just now, was stuck in the down position, the release knob would not budge, yet I was able to release it with moderate pressure
on the latch on a force vector toward the front of the car. With the seat stuck upright the force vector would then be up. Get a grip with
your finger on the metal and pull up.

Dan Shapiro
'82 5 speed

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Here's a tool that was home made by a lister to turn the seat directly on the nut when is doesn't bulge.