PCV = Positive Crankcase Vent. It lets the pressure that builds up in the crankcase out, but has a check valve in it, that doesn't allow anything back in. I don't happen to have any pics of one off hand though.
as long as you shake it and it still rattles it should be fine, i just put a new one in mine because my dipstick pops out under wot, oil sprays out, that wasnt the problem, probably blow-by, its right on the lower intake, theres a hose that goes from the upper to the lower, its plugged in the back