True there are no ports in the rear section of the cylinder head gasket. That doesn't mean that oil is not there. Under hard acceleration you get a lot of oil at the rear of the heads and lifter valley. This is why you rarely leak at the front but can easily have leaks at the rear.

I always spread a skim of RTV on the end of the head gaskets where they run up the block towards the intake area. These leaks can be pesty.

Leon