WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
Using the special tool, install the valve stem seal.
Fig 1: Installing Valve Stem Seal
Courtesy of FORD MOTOR CO.
Install the valve.
Using the special tool, install the valve spring, retainer and key.
Fig 2: Identifying Special Tools (303-300 And 303-350)