headphone slot leaking liquid

The battery should not leak. Brown liquid sounds like maybe coke or coffee. Maybe someone borrowed your phone and accidentally spilled some liquid on it.

The iPhone uses a lithium-polymer battery that has a solid electrolyte that almost certainly cannot leak. As Summer and the others have said, your iPhone has most probably had something spilled on it. There's nothing in an iPhone I know of that would leak a brown liquid.

Well it might be working for now, but for how much longer? You shouldn't wait for it to break again, but you should bring it in to get looked at, don't procrastinate on a problem that could get far worse.

If your iPhone has not been submersed in water or any liquid, you need to call your cellular provider if your cellular provider handles Apple warranty claims for the iPhone.

You should contact Apple. In India call (91) 1800 4250 744 or (91) 80-4140-9000.

I would take it in to get looked at by the carrier or Apple.