PCV valve goes into the oil separator, unless the separator is bad you don't need to replace it. Some people replace the PCV hoses as well but only do that if they're bad (cracked/brittle). The PCV valve is a PITA to get to. It took me and my dad (a mechanic) about 30 minutes with both of us working at it to get it out and back in. Mine was clogged so I'm glad we did change it.
