You'll need to pull the valve cover and pull the cam tower/rocker shaft assembly. Just loosen all the bolts slowly using a pattern from the outside most bolts to the center bolts. Don't forget the two short bolts way back by the firewall (I just remove them first then slowly loosen the longer cam tower bolts evenly). DON"T just lift the whole assembly as the lash adjusters may fall out of the rocker arms. I saw some guys mention sliding cut off rubber glove fingers over them to hold them in place. I just carefully lifted each rocker, one at a time, and pulled them out by hand and kept them in order. Once that's out of the way a deep 14mm socket will let you remove the jet valve assembly and check the o-ring.
Reassemble in reverse and I think the torque is 11-14 ft.lbs on the cam tower bolts (again, snug them down evenly in a center out pattern then torque to final spec).