Hi, I'm Not Sure What's Going On, But It Seems

Hi, I'm not sure what's going on, but it seems my breast is leaking a clear oily substance. I did not feel anything but when I undressed my left bra cup was very greasy and what ever it was started to leak through my blouse. I squeezed the breast, but nothing came out? This has happened twice before with very long periods in between. Is this something you've heard before? Thanks