Oil collects in the Subaru spark plug tube when the seals leak oil. Excess oil in the spark plug tubes can cause a Subaru engine misfire and a Subaru Check Engine Light problem. Oil-damaged spark plugs, ignition wires, and ignition coils will also require replacement.
Repair includes removing the valve covers and replacing the valve cover gaskets, and replacing the Subaru spark plug tube seals. It may include replacing spark plugs, ignition wires, and Subaru ignition coils if the oil leak has damaged those parts.