First, who's brainiac ideas was it to put a 2 peice PLASTIC intake on an engine. I had to put new lower intak gasket on 20K ago due to warping and now they are saying I might need a new intake. They say it leaks from the rear. Years ago you would just plug a leak with lots of Permatex. Will that work here? Seems like a number of you have had this issue. PLASTIC ON A MOTOR!!!

 

Your valve covers are plastic too trying to save weght any place they can thats why so much stuff is plastic!! i dont know if you can fix your leak that way..id say do your own test with Propane spray some propane around the manifold and if the idle inscreaes you have a leak. dont know much about this prob i have a 97 4.6L i have the Alumnium intake manifold