It sounds like you're talking about the breather in the head. There used to be a tube that goes from the head to the air box. It's not uncommon to replace the air box with a different air filter setup and in that case, you'll have to connect to breather port in the head to a similar port in that filter setup or to a catch tank. The idea is for the engine to suck up the oil that leaves the breather burning it in the cylinders with the gas.
Another possibility is the drain between the head and the block. They can get distorted when installed, cracked, or broken. It's made of rubber and if I remember correctly, one end is threaded. It's normally installed when the engine is built but I am led to believe that it can be replaced without removing the head.