Driver door lock cylinder(?)

[sisk61]

My driver door lock cylinder came out along with the key. I can re-insert it so it works, but it won't stay in the door unless you hold it in. I have the inside door panel off, but don't see anything that is broken or disconnected. I suspect whatever holds the cylinder in place is inside the outer cylinder. Can anyone confirm this? Is this repairable for the DIY'er?

TIA

1992 BMW 525i