Leaky Sink Drain – need help/advice

I have two delta sink drains installed in stone sinks that continue to leak. The leak is coming from the two overflow holes (one on either side) of the threaded part in the attached picture. I’ve tried teflon tape, what did work was I filled them with silicone, but that ended up catching things, causing it to get dirty and eventually partially clogging the drain. I can’t imagine that it’s the design, but more that I am not doing something, or doing it incorrectly. Any help or advice would be welcomed.

Thanks!

riderone2013-05-07 23:58:00