Case Nutty, It is a plain 580. And yes I understand it will leak air before oil,But this little hole is inside of the hollow shaft. It is about 1" from the needle bearing.I hope this helps Case Nutty. I have worked on many 580 C thru k over the past number of years, But I,m not sure about this little hole it makes no sense because oil will come out when pressure is applied. Thank you very much for any help.
Thank you, Marlin