Door locking issues

Hi all,

I've just bought my first car in peperation for my upcoming test - a 2002 Micra S. The good points are that it isn't rotten, and the clutch was replaced a couple months back. It was previosly owned by an old lady who gave up driving, and with a good service history, it seems like a good deal.

Sadly, I bought it with a catch - the driver's door won't lock. The door has been replaced in the past, as someone hit it, and even though the barrels were changed, it seems to be stuck in the mechanism. The door panel was removed when I bought it, so I have easy access, and other than that (& the common sag, but there are replacement hinges), the door is fine.

Should I try to repair it, or is it better off looking for a new door?