Many times the delay is caused by a vacuum leak in any of the lines going to the door locks. A slow leak means the pump has to run longer to get the locks to activate.

I'm not sure how to test to see if there is a leak - but if you do a search I'm sure theres info.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE