-and, for what its worth, I used the Ken-CO kit, and it worked perfectly. (yes, their parts do fit tightly, -in my opinion, tighter than necessary.)
The above replies that mention the need to get the heat away from the plastic are exactly right on target. Heat from the EGR stove pipe is the whole reason the plastic fails in the first place.
From my perspective, everyone that just replaces the upper manifold with a new one, without the modification, are "resetting the time clock." ,, tick,,,, tick,,,,, tick,,, tick,,,
(-my guess is that their next failure will be about the same mileage as the first one,,)