are you sure it is not the bypass return big line leaking at the ferrel and blowing on the jug, if not although very rare it could be the oring as posted, follow Dan's advice if inclined to check itout. Also it MIGHT save you some work to know that most exhaust manifolds are 3 piece, and IF you can get the studs out (soak overnite) use a impact and VERY lOW setting to try to jar loose. Remove the end two studs if possible and slide the exhaust manifold out so as to prevent having to take the whole thing off. Also if one makes a BlUNT 'U' shaped tool to go on the end of a air chisel set this at the bottom of the head bolts and jar them as you try to remove, if they are stuck. This works on the manifold studs as well , when you can get to them.