Ford Repair: Explorer intake leak., silicone gasket, vacuum hoses

Question
I have a 1999 Explorer w/ 4L SOHC. Two years ago I paid a lot of money to the Ford dealership to diagnose & repair a cold start problem. Now it is doing the same thing w/ the same codes, lean left & right banks. Now that I know what the problem is, I want to repair it myself. Only the upper intake gasket was replaced last time, should I replace both
upper & lower intake gaskets this time? Can some sealant be used w/ the gasket to make the repair last longer?
Thanks
Dennis

Answer
Yes, I would do both the top and bottom gaskets. They are silicone based o-rings, DO NOT use any sealant or gasket stuff of any kind, just make sure everything is clean. Glue or silicone gasket maker will cause the orings to distort and not seal.

In my opinion the dealer did you a disservice by not doing all the gaskets at the same time, the difference is only 8 bolts to remove.

Look carefully at all the rubber vacuum hoses and connections for swelling or distortion, anything thast could cause the lean code.