Looks to me like the lock is not broken but the central/electrical locking
motor/mechanic is. I experienced the same problem as what you have.
I replaced it at my '92 525i a few years ago, how I openend the door was by
pulling the inside lockpin while opening it by the remote door (un)locker.
After a while all will fail, so better replace them all, I thought around 50
Looked like the plastic mechanics wear out which are on top of the lock
mechanism, no problems ever after!
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