The crankshaft side seals fit in the groove on each side of the rear main cap and seal to the engine block. They typically only need to be replaced during a full rebuild, but can fail at other times as well. Replacement of these seals is a bit more involved than the rear crankshaft seal, as the oil pan needs to be dropped in order to access them, so it's not a bad idea to replace it with your oil pan gasket. Sold individually; 2 required per car.
Datsun 240Z, 260Z, 280Z, 280ZX
Datsun S30, S130
1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983