Squeaking cowl of a 81 z-28

I doubt WD40 would fix that and would likely only make a mess. Try a 2nd Gen Camaro forum, and see if a squeak from the cowl area is a common issue or related to a body panel seam or spot welds. I really don't see that being the case, far more likely you have a body bushing that has degraded, and there are two directly below the cowl area on these bodies. I would also be certain to eliminate suspension components being responsible for the squeak, especially sway links.