RB20/25/26 valve cover seal kit
The RB20, 25 and 26 all use identical valve cover seals. They are unique from left to right. They become dry and don't squish down as they did when new, allowing the oil to get past the seal and leak down. The oil usually runs down the exhaust side, and covers your manifolds as well as entire block side with engine oil. It's a very difficult area to clean.
The valve cover seal washers are often neglected as well. These rubber washers assist in applying even torque to the valve cover seal. Over time they also become dry and hard, and further reduce the quality of the seal between the valve cover gasket and cylinder head.
Complete set includes two valve cover seals as well as two rear cam plugs. (4 piece kit)
You may choose to purchase valve cover seal washers (picture #3) along with your seal set for a complete and proper seal.
Purchase a valve cover set here, as well as optional valve cover seal washers (yes, they are expensive, but much more elsewhere - shop around P/N 13268-58SOA)