My leak was a slow one from windshield heater under the right windshield wiper. Dripped on the passenger side of car, USA model 1985 300SD. Used a home made pressure tester. Simply made one by cutting a tire valve off a broken bike inner tube. Fitted it to a small hose with a worm drive clamp. Put hose on a small fitting on radiator from coolant expansion tank. Plugged hole in coolant expansion tank with short hose with plug in it. Used bike pump to pressurize cooling system. Not too much pressure. Maybe coolant tank cap would limit pressure. Saw leak. Confirmed leak from windshield heater visually. Bypassed windshield heat. That leak gone.