I noticed that the passenger rear door lock, when working, was sluggish and always locked after the others had finished.
This happened to my passenger side rear door and I thought it was a wiring problem so I checked all the wires in the gaiters of all four doors plus the rear door!!! The only wire insulation that was cracked was the speaker wire.

I stripped out the lock at least 5 times, each time thinking that I had solved the problem...by cleaning the contacts. However, first unlock in the morning the lock motor would be slow again. What eventually fixed it was, spraying brake cleaner into the back of the lock motor and blowing out with air(or leaving to dry).

Please see below for the pictorial how-to:

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