If you're oiling your bobbin case you're not getting oil to the place that needs it. It's the bobbin *race* that needs oiled. Take the bobbin case out and turn the hand wheel. You'll see a hook moving back and forth, the two surfaces that are moving against each other is what needs oiled. On computerized machines it's the only place that needs oiled and it only needs a couple of drops once a month or so for medium to heavy use.