Servicing the crankcase ventilation properly usually means that you have to replace all components and it can be quite expensive due to labour costs and because the manifold must be removed. It is usually said that the components for the crankcase ventilation should be replaced at least every 100’000 miles or so depending on the quality of oil, the previous service intervals and the driving conditions the car was exposed to. All plastic parts get quite brittle over time and the hoses can be clogged by old oil residues and dirt. Clogged hoses mean greater pressure, which over time can cause oil leakage. If you do nothing about the problem, it is only a matter of time before the crankcase ventilation breaks down, which in extreme cases can lead to engine failure.