2000 Cadillac Deville dash coolant temperature fanlight

2000 Cadillac Deville mileage: 105,000. I'm getting two stories from two separate mechanics and need some help here. While driving down the freeway at 60 mph, the dash coolant temperature fanlight came on and we pulled over. Lots of steam--overheating major. (I had the thermostat changed and radiator flushed 30,000 miles ago) Rolled into the gas station/shop and they said it was a cracked radiator and needed replacement. They are plastic in the Cadillac's. Next day, they called and said there were emissions coming from the radiator, as high as if it were coming from the tailpipe. They suspected a cracked block or blown head gasket and to tow it to my regular mechanic--it runs, but will heat up. My mechanic says they put water in it and drove it, it ran smooth, and they ran a pressure test and it was fine. No water in the oil (didn't mention oil in the water), and they believe its just the radiator that needs replacing, it was normal to have some exhaust coming through the radiator. In addition, I thought I noticed a little white smoke from the tailpipe when they started up the car, which dissipated in a few seconds. And, over the last month, it sounds as if there is "gurgling" going on in the dash, like water going through hoses for the heater. That sound usually happens when I start the car up in the morning, and it has warmed up for a few minutes and I am driving away. I hate to fix the radiator and then find out I need to pay for fixing an engine problem when we were planning on buying a new car anyway. Anything else I should ask them to check before authorizing the radiator work in lieu of selling it as a mechanics special.