central locking - compatability between years?

[e30_lover_CT]

In my '90, I was able to push down on my lock button to lock the car when I wasn't inside... aka didn't have to use my key to lock the doors.

My 84 325e seems to require that I use the key to lock.. can't push on the lock knob to lock unless the door is closed. My 85 325e did the same thing.

What I'd like to do is make it so the locks behaved the same as they did in my '90. Is this possible? Should later-model central locking modules be compatible with early e30's?

Thanks
Rob