I used to think there was a common key before the 751 came around, but I now believe that's not the case. The key from my '86 does not work in my '79, which is missing a key. Luckily the back of the storage doors are usually pretty easy to access. Unscrew the lock finger with a screwdriver, go out and open the door, and then you can remove the nut holding the whole lock on. Simply replace the entire lock or take it to a locksmith who can make a key. It will probably be cheaper to replace the lock.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR