The spark plug tube seal is no good, remove the valve cover, apply new tube seals and install valve covers.
VALVE COVERS Removal (Right) Remove engine appearance cover. Disconnect IAT sensor. Remove PCV valve and hose. Remove air intake ducting. Remove ignition wire cover. Remove ignition wires from spark plugs. Remove valve cover bolts and valve cover. Removal (Left) 1. Remove engine appearance cover. Remove windshield wiper assembly. Remove PCV valve and hose. Remove air intake ducting as necessary. Remove accelerator and cruise control cable bracket. Remove alternator cover. 2. Remove 2 nuts from EGR valve bracket and vacuum hose clip. Position bracket aside. Remove dipstick tube mounting nut from valve cover. Remove ignition wire cover and ignition wires from spark plugs. Remove ignition coils. 3. Remove strut appearance cover from left side of engine compartment. Loosen power distribution box and bracket. Disconnect 42-pin connector. Disconnect vacuum hose from brake power booster. Remove valve cover bolts and valve cover. Installation (Left & Right) 1. Clean sealing surfaces on valve cover and cylinder head. Install new spark plug tube seals, sealant is not necessary. 2. Using gasket adhesive, glue valve cover gasket to valve cover. Apply a bead of silicone gasket adhesive to seam where cylinder head and front cover meet. 3. Install valve cover and valve cover mounting bolts. To complete installation, reverse removal procedure. Tighten bolts to specification. See TORQUE SPECIFICATIONS table.