[C. Clark]

Hello,
Can some one please tell me about the breather / vents that are on the upper part of the cylinder head. They are viewable from the inside the rocker arm compartment with the valve covers off.
I know the one on the passenger side vents the crankcase through a hose. It's the one on the drivers side that interest me. Can they be changed and are they suppose to pass oil? Mine leaks pretty good. If changable who has them? What does the drivers side one do. I've looked through all my manuals and have only found a part # in a very old manual.
Thank you,
Chas