Blue XL-12 Oil Cap

[jclark]

Are all oil caps vented? My Blue XL-12 (1973) oil cap part #64175 doesn't appear to be vented. There is a small partial hole in the underside center of the cap. I used a twist tie wire but the hole doesn't go anywhere and there isn't any visible exit holes on the outside of the cap. Leon's parts list listed OIL CAP (Vented). With "Vented" in parenthesis suggest some are vented and some are not. I can't see how a duck bill valve could be attached to the cap either. 
Any suggestions

[jerseyhighlander]

If it is vented, the corresponding/connecting hole on the exterior would be around the edge. If there is a difference vented or not, I would guess that the automatic oil machines need the vent and the manual oiler's don't or the vent may be in the tank on some models.

[jclark]

Makes sense. Forgot to mention, it's a manual oiler
Thanks

[sweepleader]

Many oil tanks are vented with a hold drilled in on the bar side near the top.