Okay, sounds like it is a bit worn then. I suspect that when you did head they did not do guides and seals properly. You might try a can of STP/Motor Honey with oil and keep oil clean with proper changes because when oil gets dirty it increases usage. (adding to it is not the same as changing it)  

Do a compression test on cylinders. Also when doing a compression test look at spark plugs closely. If one has some strangs deposits on it thats probably the cylinder with the possible coolant issues. Also could be a intake gskt leaking and coolant being sucked into intake. this has happened to me before with a different engine set up. On compression test they should all be within about 15 lbs at least of each other.