Panhead breather fitting/case bolt curiosity...

I was looking for a leak the other day and found my primary chain oiler/case bolt had come apart where the bolt is welded to the fitting. In the process of setting it up for re-welding I noticed a notch ground into the lower perimiter where the fitting abutts the case, not ground all the way to the point of creating a weep hole, but at least halfway thru the fitting. Does anybody know why it's there? I did check an old one I had saved and it also has this same notch. Thanks Mike

My knuckle has a steel pin in the case that goes into a hole in the base of the fitting. this keeps the pipe from turning
and possibly rubbing the chain. I always figured it was used until the later breather with the rubber nipple (58)?
drinner-okc

That makes sense, of course with the stock panhead there is an elbo in the fitting that inserts thru the inner primary, which would keep it from rotating. This clues me in on why my fitting may have pulled out, over tightening to prevent rotation..... Thanks for the info Mike