Like I said, this is based on experience using one of the original Mr. Crybaby's. The new ones may have better components and and a better sealed casing.
Inside the wah, there's a slider thing attached to an electronic thing called a potentiometer. Basically an electronic 'volume' control that lets you adjust the 'wah' sound up & down. Try not to leave the wah out in the open all the time & if you travel with it, stick it inside something to keep the dust off or eventually, like old stereo systems, you'll get a scratchy sound every time you use it. You might not notice it live, but when you go into the studio it'll stand out like a sore thumb.
As far as cleaning it, experience has taught me that it's usually a temporary solution at best and not to let the problem escalate to begin with.
If you're really stuck with noise & no way to fix it, you can quickly turn the control up and down and the friction will heat up the inside of the thing and kinda 'oil' it up so that it'll work temporarily. (This works with old scratchy stereo volume controls too.... it takes 5 - 10 minutes and you have to quickly turn it up and down about 300 times before it starts working...which is really tough with a wah unless you take it apart)
There's also stuff you can get from Radio Shack, but again, it's just temporary and usually ends up making it worse.