I can't answer your question, but here's my two cents on those ball oilers. I refurbished my 13" South Bend and the ball oilers were in bad shape. I bought replacements and installed them. The second time I used one of them it failed. The ball (not really a ball, but a bent/rounded piece of steel) got stuck and I couldn't get it to pop back up. Now, I didn't like this type of oiler anyways since I think they might have a tendency to let dirt and grime get past them. They are in a pretty messy location when using cutting oil, etc.
So, my solution was to remove the new ball oilers and tap the holes 9/16"-12 since the original hole was 1/2". I made up two threaded plugs that I can screw in and out by hand. This is working very nicely for me. I know they won't fail and they don't let dirt get past them.
YMMV,
Ted