Steve:
+ 1 on Ignatio's advice about using a dremmel, and maybe some good grease, once ya get the thing off.
The seat's latch is a spring loaded rectangular metal slide pulled (to the left) by a cable coming up from the key. The cable feeds through from the left of the bike, and pulls the seat latch from the left. The latch itself simply slides over the top of the protruding U-shaped hook mounted to the Corbin's seat pan, thus locking it down. On your Corbin, this "hook" is binding against the bottom surface of the FJR's sliding latch. I guess it's pulling up on the latch, preventing it from being able to slide to the left and thus release the seat. Part of the problem is that the key can't generate enough pulling power to move the latch due to the lifting pressure of the seat's U-shaped hook on that sliding latch.
I'm thinking that maybe you need to put a lot of weight directly above the latch in the dead center of the seat between the two rubber bumpers that suspend the seat pan above the FJR's crossbar. I'm thinking that standing (or even bouncing a little) on the seat with the ball of your foot puts all your weight in a very concentrated area, and might just be enough to pop it, as someone else turns the key and holds your hand so you don't fall on your head.
Second possibility: If you can remove the key mechanism, perhaps you can grab the cable with a pair of vise grips and generate a little extra pulling power to pull that cable. [EDIT: I've never actually attempted to remove the lock with its bracket. Good luck.] Again, this will take more than one person. One of these two solutions should do the trick.
I wish there was a way to spray some lube on that latch mechanism... that might be a part of the problem as well. That might be doable, but it will take some extra brainstorming.
Good luck Steve.
Gary
