You'll have to rotate your engine and remove your breathers so you can actually inspect them.
I had a breather that I suspected wasn't working properly, was the front, I had to rotate the engine to get to it. When I pulled it, it looked perfectly fine. However, the breathers are suppose to work like a one way valve. Only allowing air/oil/whatever pass through the rockerbox cover out through the breather. They are not suppose to allow air/oil/whatever to go back into the engine.
I washed mine up real good and went old school; I just puckered up and tried blowing air through it the wrong way. There was absolutely no resistance, therefore I knew the breather was garbage.
Someone else may have a better suggestion.
Anyway, an engine rotation will give you an opportunity to inspect things that are otherwise impossible to access.