«...For most of us therefore it might be easy to condemn a non Mechitza Shul. For an Orthodox rabbi to take a position in such a Shul has long been considered forbidden by the great Poskim of the 20th century. Indeed, my own Rebbe, Rav Ahron Soloveichik forbade it. As did his brother, the Rav. But the issue is not as simple as that.
For starters, I want to make clear, that I in no way endorse or permit Traditional Shuls. Halachic opinions on this subject are way beyond my pay grade in any case. But they are not beyond the pay grade of at least one Posek of the 20th century – who differed from the above mentioned Poskim...»
The Mehitzah Heresy - Emes-Ve-Emunah - Jewish Ideas Daily
Many OU shuls with RCA rabbis in smaller communities had various compromises re: Mechitzah. A Common one was tripartite seating. Another was separate but without a Mechitza, which still prevails today at many Orthodox weddings and funerals.