The lock for the FZ6 seat is right above the rear wheel, crap off the wheel can cause the lock to seize up, when I had my one I greased up the cable and made up a cover using a bean tin to deflect the crap off the lock mechanism. Does your key turn in the lock as it my be the previous owner never used it and its corroded up, might be worth a squirt of something to try free the lock off.