Front doors will not unlock

I had a 1999 and now a 2005 Park Ave Ultra. The door handles get corroded and rusty so when the handle is lifted it doesn't spring back internally. Check and see if you can lock and unlock manually from the door panels. If the rocker style mechanical lock doesn't easily and audibly sound like its locking and unlock then its stuck internally. On the drivers side , use the key and use light pressure toward the unlock position while lightly pounding with your palm around the area of the door handle. In the end you'll have to replace the door handles.