I'm not a body/metal man but I think I'd pull off the center strip, run a nice bead of sealer down the middle and then reinstall the center strip....and of course put a dab of sealer where the anchors for the center strip come through.
.....I might ask, are you sure its from the center strip or is water on the valve cover coming from a mis-aligned drain hose for the cowl vent? Just had to ask.
