Incidentally, when the driver's side switch "fails" it's usually the passenger side switch that's the problem. This is because the use of the driver's side switch requires that the neutral position on the passenger side make 2 separate contacts. The reverse is also true for the passenger side switch. The switch in position only requires one contact, and is under more pressure, so that way, it generally works better.
This is done so that someone pressing one switch down, while the other switch is up doesn't result in a short circuit, just the motor doing nothing.
Clean the passenger side switch first. It's easier, and more likely to be the problem.
Edit: Also make sure to use dielectric grease on the contact bars, or you'll be doing it again in 3 months... Ask me how I know...