You might have a grounding issue with the power locks, or the switches could be bad.
As far as problems with the Zetec, the biggest one is the thermostat housing which is made of plastic and will leak. I would replace that with a metal Contour housing to avoid any problems there. Motor mounts go bad, but as long as you have replaced them with OEM, they should last a long time. Other common problems are the swaybar endlinks and strut mounts. Other than that, these are very solid cars and as long as you keep it maintained, it will last forever.
I like your SN, do you have a daughter named hitgirl lol (Kick-Ass movie reference).