I'd use the least amount of water/liquid possible to avoid
water spots. Headliners seem real susceptible to them, and you can easily get a nice water ring around where you cleaned. You may even need to gently use a steam cleaner (rug shampooer) on the entire headliner after removing the spot to make it look right. I have used mine several times with no ill-effects. But I am careful not to soak the headliner to avoid any rings appearing.
Dave