I did this quite some time ago, but if you’re that way inclined (like me) it’s quite interesting.
The main door wouldn’t shut and was blowing open during services which is certainly not ideal in the winter!
All that was needed was just a good clean and grease of the parts and it works fine. Here are some pictures showing the lock in various stages of repair.
The face of the lock removed from the door
The rear of the lock
The wooden and metal parts of the lock detached
An internal view of the lock (the interesting bits!)
All safely back on the door and working
I couldn’t have done it without my trusty helper!