With only one breather, you are letting unmetered air into the system, and potentially causing a lean condition. It is better to have the entire system working, and if oil is a problem get a pcv valve for a supercoupe. If that doesn't work get a catch can. If you really want to go with breathers, you need them on both sides, but this elimnates some of the backpressure on the rings cause by the pcv system, which help seal them.