Some late model Subarus and all earlier models have a Crankcase Ventilation System which does not use a PCV valve.
For a description of the system, as well as procedures for component removal and servicing, see Section 4.
The only regular check necessary is an inspection of the PCV hose(s), which run from the crankcase to the air cleaner. These should be checked every 12 months/12000 miles (20,000 km) on 1970–73 models, or every 24 months/24000 miles (39,000 km) on later models. Be sure that all of the connections are tight and that none of the hoses are pinched, clogged, or cracked: replace as required.
On ff-1 models, the oil separator should be cleaned every 12 months/12000 miles (20,000 km), whichever occurs first.