Wondering if this is good for a quick fix, or if I'm looking at a major repair. 2004 XC90. Unlock the car, all doors but rear driver side unlock. I have to get in, lower the window, and let my son unlock it himself from the outside. Seriously almost drove away on him once; he's 9 that wouldn't be good. But when I lock the car, all doors lock. All but the driver's door are missing the circular "ring" that goes around the peg, don't know if that makes a difference.

The fact that the door locks when I lock the car leads me to believe that there's a chance it could be a simple problem. What say the experts?