Hemikiller has it right. Frankly, I am a bit surprised at how many of my customers don't know about Ford's "twist-in" pcv grommet. It's been around since '68, I think. Here's the deal...…...Ford, in their infinite wisdom, realized that it was costing them additional stampings to stamp out two different valve covers, one with a twist-in for the oil fill/breather cap, and one for the pcv. SO, Ford started stamping only the twist-in cover, and supplying a simple rubber twist-in grommet for the other side's pcv valve. I've seen so many butchered valve covers because some owners ( and some mechanics) didn't really know Fords. Every Mustang/Ford parts supplier has the grommet though, and it's real handy. Then again, there's those guys who render the pcv system in-op like they expect to gain horsepower or something......