As an alternative to Jim's solution, I purchased and installed a remote to lock and unlock the car. The kit was around $30 and took awhile to install, but was way cheaper than walking into the dealer's door and buying the proper part. I made the change about 2 years ago and it has worked flawlessly since then. This was on both the 190D 2.5 and the 190D turbo. In a pinch, you can still open the car with the key from the trunk lock. The only way to pin this problem down though is to remove the driver's door handle and you will see the arm that is broken. It will be obvious.

Tom

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1993 300TE
1984 300D
1984 300SD
1976 BMW R90S