Heater core cleaning?

I just went through this with my 68 Barracuda. My core had some scale on it, far less than your's does and yes it had a leak. I suggest that you take it to a radiator shop and have it professionally checked, believe me you only want to reinstall it one time. If it does have a leak they can either fix it if it's not too bad or re-core it which they are capable of doing, or get a new one which is the route that I chose to follow. I bought a new one from Mancini's and it fit perfectly.
Bob