There are three OEM options for the AD that I know of.
First is the small open element dry type:
https://www.flickr.com/photos/advance-design_parts_co/8250844197/in/album-72157632186114015/
https://www.flickr.com/photos/advance-design_parts_co/15614673146/in/album-72157631868452754/
Second is the small oil bath common to the Thriftmaster Series it is called the 1-pound (some materials call it 1-pint) in the Salesman Data Books, R.P.O. 216D on a 3100.
https://www.flickr.com/photos/advance-design_parts_co/16336222880/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8129088452/in/album-72157631867396207/
The last common to the Loadmaster Series is this, referred to as the 2-pound (some materials call it 1-quart) in the data books, R.P.O. 216E on a 3100.
https://www.flickr.com/photos/advance-design_parts_co/12315093845/in/album-72157640522200463/
As Tim refers to here is the PVC equipped style.
https://www.flickr.com/photos/advance-design_parts_co/8129417263/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8129442056/in/album-72157631868452754/