Benjamin rear sight adjustment

Wasn't really looking but found a mint condition Benjamin 397PA with nice walnut stock at a great price. Shoots great, but noticed the rear sight elevation screw was missing. On my 392PA, which also shot a little high, I had to remove the screw and tape the sight leaf to the compression tube with a couple turns of black electrical tape to get it to shoot to point of aim at 33 feet. Now with this new rifle, a virtual twin of the 392, the sight spring is actually sitting flat on the sight body; in other words, it cannot go any lower. Still shoots 3/4 inch too high at 33 feet. Both guns are in pristine condition, with barrels tightly soldered to the body. How can I make the 397 shoot to point of aim, with no vertical adjustment left?