Installed ballvalve for water heater drain year and a half ago. Just tried to open it--wouldn't turn. there was a shiny, fairly thick, black hard deposit on the stainless ball inside the ball valve, perfectly contoured to the ball, preventing it from turning. Anyone have any idea what's going on? Feels like hard plastic. Came right off ball once i opened up the guts. 10 year old gas water heater.