valve cover grommet for twist-on cap

One of the Mopar gromments worked on the PVC, but was too small on the breather, I recently ran into this issue and ended up slicing and dicing a gromment on the breather and still couldn't get it to work, thats when I decided to put in a PVC valve without the guts, making it open all the time, worked fine. I hope your covers dont leak, Im having issues on the back of each head leaking.