AIG,

Thanks - I figured it out after you explained how it worked.

Apparently the locking 'PIN' wasn't lining up with the hole in the gas lid.

I got to looking around, and the tether that holds the gas-cap to the car was spun and twisted so bad it prevented the lid from closing all the way. When you went to lock it, the pin would then mis-fire and wouldn't make a positive latch.

I 'unwound' the tether, and now the door lays nice and flush with the body and the locking mechanism functions again.

Thanks for the help,
Shawn