Hi Toltyk,
Came across your post searching for solutions to an issue I am having. I don't own a Raptor, full disclosure. Just an F150 with the 6R80 transmission. Got it about 6 months ago when my Dad passed. '09 with 128,000 miles.
After driving it for about 6 months, found a puddle of tranny fluid in my driveway. My stepmom had several services performed on it before she gave it to me, and one of those was new trans fluid/filter. I thought maybe the gasket was leaking.
After more research, I found that the bulkhead fitting on the passenger side is a common leak point. Lots of videos on that. Mine was for sure leaking from there. But very sporadically. It will go 500 miles and not leak a drop, and then decide to burp out a 1/2 cup or so. Only happened a couple of times.
I'm thinking that vent you are trying to modify is possibly my issue. You mention they can "clog up" or the little rubber valve may stick. If that is the case, I would imagine the pressure inside the trans case will force fluid out of the weakest point. In my case, the bulkhead fitting.
Just wondering if you ever completed your efforts to modify yours.
Thanks,
Dave