vacuum lock problem on 1987 560SL

[domchang]

Hello All,

I have this strange problem with the passenger door lock on a 1987 560SL.

I can unlock it from the driver side door central control just fine, however when I go to lock up all the doors from the driver door lock using the central locking system, it fails to lock the passenger door lock!

I thought it was a vacuum leak but then I would not be able to unlock using the central locking system would I?

I have to go, manually lock the passenger door lock with my key and then it locks.

One thing I did notice, once I've activated the central locking system, I can go to the passenger door, open it, lock it using the key, close the door...I then hear two or three popping noises and the door then locks!

any ideas?

dom