i had the exact same problem with my 1262's, i tried the mister gasket brand but the coolant passage was WAY to big so i stuck with the 1262 and got some .030 wire out of my mig and made four "o" rings that i rtv'd to the head then rtv'd the gasket over the "o"rings and torqued everything down, seems to be working fine, went thru 4 sets to get this far, every time mine went they washed down the number 1 and 5 cylinder with water, even pulled the heads and intake and had ALL of the surfaces "cleaned up" milled and the problem still persisted, might be a problem of thermal expansion loosening the fasteners and coolant pressure builds enough to lift the intake, make sure to retourqe the intake regularly, i do mine once every two months