they make breathers with baffles in them to keep that from happening but i'll tell you with boost you still get some in there. i have to wipe my valve cover off all the time by my breather. and i welded a baffle in mine to prevent that and it still comes out there .
There are some brands like Moroso that make baffled grommets.
I'm getting a properly welded billet filler neck with a baffle welded in made up but in the mean time this type of grommet has worked for me.