You will need a new plenum gasket, or if you choose to try and re-use
the old one you will need some black RTV. Apply a THIN coat of the
sealant to both sides ot the gasket. You must pull the plenum to change
the rear plugs. Torque them to spec and apply anti-sieze to the threads
prior to installation. Do not remove anything until the engine has
cooled so you do not gall the threads when removing the plugs.

Chris