If you see oil pooling around the intake, you'll know why. Not saying you will, but it's a possibility. Sometimes oil will wick up the threads and form little puddles in the intake cavities. I always use sealant.
I've done the intake several times but never had it leak there. Where the silicone goes across the face of the valley, yes. Usually the oil seeping onto the intake is because of the mating of the valve covers and intake runners. I have my valve covers ground down so they sit flush.