Insert a thin screwdriver under the plate for the interior knob and twist enough so the the knob plate separates from the mounting plate underneath. Twist clockwise on the mounting plate to slide it off from the preset screws that extend from the inner mechanism.
Pull the exterior knob from the front of the door. Unscrew the bolt from the side of the door and slide the plate and bolt from the side. Check the inside of all the pieces for any broken or bent parts. If any parts are defective, call Weiser customer service at 800-422-4278 to check if replacement parts are available.
Dip the toothbrush or swab into the alcohol and scrub away any dirt and debris. Pay careful attention to where two pieces of metal slide over one another, or where any movement at all is discovered in the mechanism. A toothpick may be needed to pry out stubborn bits of gunk. Continue to clean until the inside is as spotless as you can make it. Dip the key in the alcohol and slide it in and out of the keyhole three or four times to clean it.
Lightly coat the lock mechanism with a commercial lock lubricant. Do not use light machine oil if you live in a dusty or four-season climate, as it will hasten the accumulation of dust inside and then solidify during the cold season.
Reassemble the doorknob by reversing the steps. Test the key several times to make sure the latch is opening and closing fully and freely, with the knob turning well in both directions.