not to repeat what'* already been said, but.
wait, i'm going to.
it'* most likely the upper intake. happened to my grandfather in law - i went and replaced it - and we spent a fair amount of time pouring over the old one and never found the leak. gasket was in good shape. we replaced the upper intake and haven't had a problem since...
there'* a lot inside the intake (which is a big part of why it'* a composite to begin with) that you can't always see - so don't assume that you're intake is 100%, cause you can't see 100% of it...
96 LeSabre (L36)
95 Olds LSS (L67)