Well if you could make it work everytime by hitting the clean button I would rule out gears and look at the switch. There must be something in there not allowing it to stay in complete contact with the wiper motor. You can get the switch from your local Chevy dealer for about $40 and it'd be a ton cheaper than a new motor not to mention much easier to install. Take out the switch and jumper the wires to see if you can make the wipers work.