Indy once told me a slipped liner presents just like a failed head gasket - my engine is a little "tappy" and uses a little coolant but the needle stays very firmly at 12 oclock and I have done two or three block tests over the years which have been negative.
Get that UV dye and drop it in the coolant. Give it a few days and then shine a UV torch (eBay is your friend there) on the dipstick. If it shines then more than likely the head gasket is going and that might be the tick / chuff.