Before you buy another switch, try spraying electrical contact cleaner into the switch and then cycle it several times to clean up the contacts. Do this a couple of times, after you remove the switch from the door panel, as its much easier to get the fluid into the side cracks and seams of the switch. Be sure to wait 5 minutes to let the fluid evaporate before turning on the ignition and trying the switch.
Unfortunately, you'll have to remove the inner door panel to remove the switch (as its screwed into the door panel from under neath. You'll have to do this anyway if you're changing the switch. Good Luck!