We’ll you’ve helped me discover something interesting. I have two ZF5s in my garage, and I looked all over them and couldn’t find a vent. Then I did some internet digging and it turns out the zf5 vent is in the stub boot! It’s a little half-moon cutout, I took a picture below:
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The problem is that the new aftermarket stub bolts don’t have the vent. I looked between all the folds of the one I just installed and couldn’t find it. That means I need to add a vent somehow. I sure wish I would have learned this when I had it all open and apart! I could have easily drilled and tapped the case to add a vent. Maybe I’ll just make a little cutout in the boot like what came stock on the truck.