Try this, put the key in the lock, now rapidly pull & push the key as fast as you can. You only have to move it back & forth about 1/2". As you're doing this turn the key to see if it will open. Turn while you're doing the sliding in & out. I've opened some locks with a non matching key this way, worth a shot.

Before you butcher anything up or ruin your paint just drive it down to a locksmith and have him open it.

DO NOT use WD40 on the lock, there is a reason real lock lube isn't a liquid. If you feel the need to try something anyway go to Home Depot and buy lock lube, it's usually by the towing accessories.

UPDATE

Powdered graphite = FAIL
WD-40 = FAIL
Push, pull, wiggle wiggle, twist = FAIL
Lightly tapped with a screwdriver and hammer = FAIL
Flat screwdriver in the slot and turn = FAIL
3/8" drill bit through the tumbler = SWEET SUCCESS

I musta had 5 layers of masking tape around the lock and nothing was damaged. I got impatient and didn't wait to try and get a new key made. Now I need to install a new lock.

Guess I'll never really know what happened ---Oh well!!!

Thanks for all the great suggestions.

Sorry to hear that you had to drill out the lock but it's an easy replacement. Glad you were able to break in.

Drilling works but they're easy to pick. I forgot the keys to my Road Runner once, 3 hours away at the drag strip. My son had the trunk open in 3 minutes. Had the steering key lock done almost as quick. Him and his brother used to try and open old file cabinets when they were kids and taught themselves to pick locks.
Doug

I haven't bought one in a few years, but you should be able to get a new trunk lock kit at NAPA. It come with the cylinder, 2 keys, and assorted levers that go from the lock cylinder to the latch mechanism.