1998 Cadillac Catera Coolant Leak and Smoking

I just purchased a Cadillac Catera and its leaking coolant and smoking--i have added coolant however there has to be a leak because-this only temporarily stops the smoking and the leaking begins again-Since adding coolant "only" doesnt fix the problem -im taking it to the automotive repair shop-but I dont want to pay more for something I dont need nor get something minor done when it may be more serious-please tell me what 9/10(probability) it could be-i, e-will I need a tank(s) replaced or whole radiator?-Thank you so much*-