Help with a Leak under the car.

I am a novice. I have a 64 plymouth valiant signet with the slant six. I have a leak that has gotten worse. I use to have a service manual, but unable to find it. The leak is coming from the seam of a compartment behind the engine. I am not sure if it is oil, transmission fluid or brake fluid. I noticed that the brake fluid had gone down, since the last time I filled it about two weeks ago. I know I am probably not given enough information, but I thought I would take a chance. Thanks!