2004 S80 Volvo Driver door locks

I have an S80 volvo, the driver door lock keeps going up and down, I have to open the door in between the up and down. (tracks and retracks) My father told me to put wd40 in the key hole that worked for a short period of time. The volvo dealership stated it will cost me close to 400.00. Yikes. This is not the first time this happen, I got it repair twice under warranty. Please help.