I would do the easy things. Put some graphite on the key & lubricate the lock.
After unlocking on the fob does it open manually on the inside?
Does the drivers side always unlock.
Changing the fob battery can't hurt.
With the lower door card off you should see the central locking moving the rod going to the door. If it works I guess the lock is sticking. The actuator is in the centre between the purple boxes on Dave's photo
The card comes of by removing the screws on the side & bottom of the door.
https://www.tm-img.com/images/2026/09/07/Morgan-loose-fittings.png
