There is a large round black cap on top of valve cover that is hissing. I cant figure out how to get it off to replace the gasket. Tried turning it hard both ways no luck and also tried pushing in little tabs and won go. Help

 

You can only replace the whole plastic unit! Be careful when you remove it there is a plastic hose that attaches to the bottom! Most times the hose is broken and causing the hissing sound! Sometimes it is the breather but that is rare!

 

Its definitely the breather and seen another thread where someone took it off but didnt say how