The book time on the job is about 16 hours of labor. Now that time was established when the car was new, by factory trained mechanics, with all the special tools, and in perfect working conditions. Plan on two or three times the labor if it is your first attempt on an old car. Otherwise check to make sure it is not the heater valve o-rings which can be replaced in the car. The heater valves are behind the ash tray. If it truly is the heater core, try Bar's heavy duty stop leak (brown with little plastic like pellets), scary, but it really works and does not seam to cause any complications.
