If you have to use the manual release each time you buy gas, the lock is locking, but will not unlock. If the lock did not work at all, you would not have to release it all the time, it would stay unlocked.

Open the gas door and have someone lock and unlock the doors. See if the pin goes in and out.

Look carefully at the grommet around the pin, it looks like nylon or plastic, but it is actually rubber. On one of my cars, the grommet was not installed fully, pushing the pin to one side, causing it to jam. Seating the grommet freed the pin.

Next you can remove the three fastners that hold the center plastic piece around the trunk latch and pull this piece up and off the sill. then remove the three fastners that hold the right side of the trunk liner and pivot this piece toward the center of the car, giving you access to the door lock itself.

The rest relies on your troubleshooting skill.
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3 8s & 2 7s 725,000 miles total