Thats true WD-40 won't make anything rust, but it is not a lube. It might free up your cable if it is rusted inside because it is a penatrating oil. If you notice it when you spray it it bubbles this is what makes it work it way in and free up rusted parts.

 

I have a magura hydrolic clutch and it is about as nice as they get. If you want it easier buy a hydrolic clutch either one billitanium or magura.