After replacing the coolant and fully tightening the grain cock it started slowly dripping from it when the car warmes up.
Did not leak at all before I opened it to drain coolant, now no matter how tight I close it come coolant still gets out when hot.
It leak right from where it grains when opened. Any experience and ideas? Thanks!

Replace the O-ring.

if that doesnt work, make sure you didnt strip it.

Only one ring?