pcv valve test. on 1996 GMC Sonoma

How do I check pcv valve to know if it is operating correctly? I have a sudden engine oil leak coming from near the rear of engine and is a considerable amount. It may be main seal or oil pan leak. Thank you.

Asked by for the 1996 GMC Sonoma
with the engine running. there should be vaccuum at the valve. it removes excessive crankcase pressure and re burns it in the intake system. if it is bad, it will cause a leak and the rear main is a common leak point.

How is the best way to repair this leak? Thanks.