[Pops]

Hello fellow truckers. I am new to this forum and happy to have found it. I own a 66 GMC. It's an inline 250 with a 3 speed. It's been modified mechanically but it looks, sounds and drives as an original (I think; lol).
I've always loved trucks but this is my first classic. I am still attempting to learn what is wrong with it vs. what is the-nature-of-beast. Especially when it comes to various sounds.
Since there are many days, hours, and topics to cover, I will attempt to write on one issue/topic at a time.
My first question concerns the axle air vent. Looking back from the cab, its on the right axle tube; its about 3/4 inch tall and it's shaped like a mushroom (dimpled on the sides of the so-called cap).
QUESTION: Being a conservative, I'd like to know how to verify that the vent is doing its job without breaking it. It looks to be clogged with black paint as one of the PO painted the entire undercarriage. What concerns me is that it looks so simple to remove, and clean, that I can't help but believe something will go wrong if I just reach up there and break it loose. What risks are involved if I remove; does it take heat; PB blast; etc.? If I break it am I going to lose fluid, etc. If I don't remove, could I just put some heat to it and use a pin to pick the gunk out of the mushroom/cap.
I'm a family man who loves God and Country. Pops