Ok I am in the beginning of the build of my 1979 XS400. I am in the stage where I am cleaning things out and trying to start it. My problem is that I cannot get the darn seat to open! I see the key lock under the rear of the seat, it has HELMET on the right and SEAT on the left. I am guess I put the key in and turn the key lock to the left to open the seat. I tried this and couldnt unlock the seat, I even sprayed PB Blaster in there to try and free up the lock (it has been sitting for at least 20 years). If the lock is frozen how can I get the seat off of there? Please Help Me!!!!

Have you tried pushing down on the seat while trying to turn the key. Don't force the key as it will break inside the lock. Tony

if you can't do that, the other way is to undo the seat opins on the other side, very fiddly!

You might try an m-80.