Three things cause fluid to burp out the vent.....Way too full, way too hot, or sudden decel forces fluid up front to the pump area.
I used to have the vent leak when drag racing on a real short track with a "real" short shutdown which required LOTS of brakes.
Did you guys use new sealing washers on the pump bolts? I've had a few leaks from around those before.
Otherwise the only place it's gonna leak is from the convertor seal/bushing, or the oring around the pump. Not much else left.....