Talking about the radiator, you can open your engine and check for any kind of leak in the radiator. there are small plastic caps on the radiator, there may be a leak from there. If yes, it means your dealers are right and you need to get the radiator replaced. And in case of any replacement, you can get your car scanned at any local workshop as well tocheck any sever problem. If the warranty of your car is already expired, then you may take your car to the local dealer which will be way cheaper than your dealer.