Saab 9-5 6 cyl 1999 coolant leak?

Need some help please. A few months ago I bought this car for my son. 72,000 He has driven less then 200 miles and I have spent 1500 in repairs already for broken control arm.
Now there is a coolant leak. He was driving and the check oil light came on, he stopped and checked the oil, barely a qt low. Added oil and back on the road. Next day oil light comes on again and then car starts to smoke, he pulls over. Car has coolant coming out of bottom passenger front side. We have the car towed. The mechanic called today says it needs a radiator. Cost of repair $700. He said it is a seam leak. Before I dump more money into this lovely car could there be an underlying reason for the seam leak? Why was the oil light on? I am not dealing with a mechanic I know so I am worried about paying for something that I may not need. The mechanic does have a 5 star rating from Tirerack and AAA.
Thank you.