I've seen similar behavior on my car, but if I move the passenger lock a couple of times manually, before using the automatic locks, it locks fully.

It looks like dirty joints in the lock linkages, maybe grease with dirt picked up over the years?

I'm planning to open up the door panel, clean and lube all the linkages, then put it all back together and see how it works.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...