The central locking system on our 1987 190E 16V intermittently delays a few seconds longer than the normal (immediate) in unlocking from either door and the trunk. Is this a sign that the central pump is beginning to fail? Given that this is an intermittent condition, any way to test?

If the central system fails, can a single door or trunk still be opened with the key?

Thank you--Jim Herold

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Jim Herold--Current: 1987 190E 16V, 1999 ML 430--Past: 1971 280 SL, 1972 250