"Use an exacto blade to clean paint build up on the edges of the holes."
That's a recipe for future rust as you're likely to cut through to the metal.
If the rock guards are new they normally fit easily but a little glycerine or silicone grease will do no harm. If they are old or you're reusing the original ones, you're in luck if you still have all of the teats and/or the remaining ones haven't split where they mate with the wing. They are MUCH easier to get in than out!