E24 servicing in Dublin /door deadlock?

Hi All - a new member here, with a 1988 635CSi acquired last year. Car generally in great nick but naturally enough requires ongoing maintenance - hence looking for recommendations for a good indie mechanic who would know their way around these beasts, in/near Dublin. Suggestions much appreciated.
There is a specific problem I’ve been unable to resolve too - driver side door deadlocked and won’t open, from inside or outside. Central locking continues to works across the passenger door, boot and tank lid as normal. Anyone come across this? It’s possible that something is faulty, but I fear it could be a “user error!” I’ve read this deadlock may have been an actual feature but can’t find any way to undo it, save from dismantling the door. Perhaps I’m missing something though?
Many thanks!