i would tried graphite, but its probably too far gone to have been of any use anyway. the drivers door cylinder sometimes get too worn out if not kept lubricated, especially since it is most used. in my old e30, it was easy to lock, but difficult to unlock. and if double locked, forget it. to fix it you can get a cylinder repair kit from bmw, should be less than $100.
in my old E30 i stopped using it when it got worn out, and used the trunk instead. in my current E30 i spread it out between the trunk, drivers, and passenger door, and also keep all the locks lubricated.