U.S. Plastic Rifle Butt Oiler Incorporating A Grease Pot

I recently came across this U.S, plastic rifle oiler oiler with a small built in grease pot on one of the end caps. I have a very similar plastic oiler but without the grease pot attached and this is the only oiler design that I recall seeing with provision for grease specifically built in. I did not really purchase this item out of it's military interest but mainly for it's neat and interesting design.

I don't know how common these oilers are with the grease pot but it is the only time I recall seeing the provision for grease included. I guess that you could easily miss the provision for grease unless you look carefully. To access the brush and pull through you simply pull the cap off the tube and to get to the grease you unscrew the cap. The really neat part of the design of the cap is the anti-rotation "splines" on the cap which stop the outer part of the cap from turning when un-screwing the inner part to get to the grease.

How common are these oilers on the Milserps scene?