Well, at least you know why your intake was leaking
Helicoil is a fix
OR
Replace 3/8-16x1-3/8 (?) with 7/16-14 or 7/16-20
(tap will cost you $12 +/-)
OR
Another option is JB Weld a stud in place but then you have to slide the manifold into place over the stud which can be a PIA
Thats why the military doesnt let me tap aluminum, shyt happens
Good Luck