I am sure this trick has been posted before but I found this simple modification to my machine tool oilers to work very well. Adding a Buna N No. 6 O-ring around the slight groove on the nose of the pump oiler provides a better seal to the spring loaded ball oiling points on the machine tools.
Below is an example of oiling the ways to one of my metal lathes.
I also use a colored cable tie to identify the pump oiler based on the color of the cap to the oil container.
Thank you for looking,