Sorry, my lathes are later models that don't use those direct oiling tubes.
Personally, I would be hesitant to obstruct those tubes with felts. There's no guarantee
that they will actually slow drip, or even do so after a period of time. The only way that
you will know the parts are getting oil is if the tube actually empties. You really don't want
a felt to hold and keep the oil.
In regards to frequency, if you use the machine almost all day, then I think once at start of the
day should be sufficient. You might do some tests with your oil on a part that you can view
easily....maybe reversing gears? Coat the parts with oil and then see how long it takes before
you think they need oiling again. This way, you know what's happening down in your apron
and how often they might need more. The only other way is to setup some sort of drip system
which sounds like a major pain.
I'd rather put up with oil drips than to take a chance on a blocked tube. Just part of the joy of
having an old SB lathe I guess.
PMc