My garage found a small amount of dried coolant on my radiator and block heater and tell me that I needed to replace my radiator, block heater, and hose urgently, as it could leak at any moment.
In order for there to be coolant residue on the outside of places that it should inside that is clear indication that there is or was a leak. Also, seeing the flaky, dried up build-up is an indication that the coolant has been leaking at that point for quite some time, in order for it to build up into the pile you see.
If you are checking for the leak while the vehicle is cold and in your garage then this is not the how it should be checked. A small leak [like the one being described in your post is going to be present only when the coolant system is pressurized.
If the system is cold (sitting overnight or long enough where the engine is equal to ambient air temperature) then it must be pressurized using a device called a Coolant Pressure Tester. If you were to purchase one of these then you must make sure the adapters for it are for your specific vehicle. There are many different styles different make and model vehicles.
If the system is hot (at normal operating temperature), and the leak is big enough, then you might be able to visually see the leak. If not, then you will have to wait until it cools down (in order to ensure that there is no excess pressure in the system) and then pressure test it.
Once you've identified where the leaks are then look into replacing those components.
It is never recommended to use any type of radiator sealer additive. These products tend to raise the pressures in the system causing more strain on the surrounding components involved in the system. They also, will deposit themselves wherever they land in the coolant system (not how they make it look in the commercials where it goes directly to the leak and creates a perfect patch).
The reason why they make it look the way it does in the commercials is because in a perfect world or a controlled / simulated environment then that's how it would work out. In theory the liquid should take the path of least resistance. In this case, that would be the point of the leak. But, different vehicles handle their cooling differently and it's not a "perfect / simulated environment".