I am in the process of rebuilding my 1989 3.0 Montero. I have the new heads, head set, head bolts, and timing belt. On beginning the re-install I went to replace the o-ring on the tube the leads from the heater core to the rear of the water pump and goes under the intake manifold. The one that comes with the head set is a normal round o-ring. The one I took out is more squared off and fits tightly whereas the aftermarket one fits way too loose. I then went to the Mits Dealer and looked it up and it showed the same one. No way am I going to put this together and have to pull the whole engine back apart just to fix this o-ring again. Has anyone had this problem and know the proper part #? Maybe someone has replaced it with a squared off oring and I will have to check the local aftermarket. PLEASE HELP!