Denny, you were correct, the breather was threaded. Came out easy and the metal cleaned up real nice with some kerosene. The top felt loose but the shaft was completely clogged.
For what it's worth, the plastic replacement doesn't come close to fitting. I suppose in a pinch you could drill out the original hole and press it in.
http://farm3.staticflickr.com/2805/10169122335_8a036a8a85_c.jpg
