Yes, WD40 is not really much of a lubricant, it gets rid of water. Since you're already having some difficulty with it, I'd try a bit of penetrating lube (e.g. PBBlaster). Once you've got it working reasonably smoothly, you might try something like Boeshield T9 to protect it (that leaves a thin waxy-type coating after its solvent evaporates and should help prevent new rusting).