for some odd reason toyota didnt cast a lug on the top of no1 port for a stud. so there is not a lot holding the manifold at that end.
as such they warp and/or pull the bottom stud out or rattle it loose. causing more warpage therefore ruining the manifold.
the facelift/superceded part has an extra lug and you just put another stud in. there is already a hole there in the head for it.
we'v done about 5 here alone. and iv supplied 12 to a place in auckland....