Too much pressure in the engine can force oil out past the fill cap, but unless you made the clogged screen worse than it was it should not happen. That rubber grommet does just pull out but it is for sure old and hard so expect it to break if you try removing it. Those vents are hard to clean by hand, best is to soak it in some good de-greaser or use a parts cleaning tank if possible. For all the effort it could be cheaper time and material wise to just find a good used one to swap out.



