key goes 1/2 or slightly farther (not as far as ign).
if the lock cylinder starts to turn (tumblers in correct position), the problem is not the lock itself, but the latching mechanism. if not turning, the lock is the issue.
Lock issue. as stated already, some lube may help. use a good penetrant if you can. once you get it open, continue to the next step.
latch issue. ok, this is the biatch to fix.. as you have to get the damn cap open in order to fix it. once you get it open, remove cap (2 screws, dont loose o-rings). disassemble the latch assembly. once the latch assy is off the lock cylinder, there is a metal plate that needs to be removed, should be fairly easy to remove. under that metal plate is the problem. the gas/ethanol fumes cause corrrosion in the sliding part of the latch and the groove it rides in. remove it all, clean it up, a little grease of some sort and reassemble. While the cap is disassembled, now is a good time to also clean and lubicate the lock mechanism. use graphite lock lube for the this, after cleaning it out with the cleaner of choice.
wow, a run run run run run on paragraph.. well its early and I am not yet awake.
I just had to do the latch on mine (on monday in fact). I was lucky enough to get my key out while lock cylinder was in a position where tumblers where still correct (dont ask, it took some doing). I stuck a 3/16 (I think,might have been a little bigger) flat screwdriver into the lock, and with the added leverage that gave me, I was able to open the cap. YMMV