I have a 1990 golf 1.8 8v. It has 250K KM on it. 3 weeks ago I switched to AMSOIL 5W50 and ever since it is leaking oil from the back of the engine. There is always a oil spot under my car ( cap full worth) it only leak while it is running. I have already replaced the valve cover gasket. The oil leak is from somewhere back of the motor. I cant figure out where! Is it worth adding an over the counter leak stop additives? I cant use ARX since the oil is only 3 weeks old. I am not about to waste $50 worth of finr synthetic oil and Mann filter.