The leaking radiator is a known issue and quite common. Mine never overheated, the only clue was a consistent, slow drop in coolant reservoir.I live within four miles of an Alfa dealer located in Glenview, IL that opened in the last year or so. I went there to get an oil change that was surprisingly expensive. I received a message from someone at the dealership after I had picked up the car informing me that they found a small leak in the radiator and it would cost a bit over $2,000 to replace it. That was four months ago and I have seen no evidence of any leak nor has the temperature ever risen above normal in all driving conditions. Needless to say this has left a bad taste in my mouth, though all previous dealer experiences were average at best. I love my car but the dealer situation is awful. Given Alfa's niche role in the U.S., you can't afford anything less than great service priced fairly.
The only way to see the leak on mine was by removing the undercarriage trays while changing my oil. Mine was repaired under warranty.
Feel free to pm if you have any questions.