8 1/4 vent tube

It looks factory from what I can tell in the pics and it appears to be an 8-1/4 but more pics would be helpful.

Do not plug it up. That's the vent. Plug it and it'll puke fluid out when you drive it.

No the vent I recommended earlier won't work without tapping threads into the case and if you do that metal will get down inside and trash it. Do as I said in my last post. That's simple enough, isn't it? I bet I could do it in 15 minutes.