Leaking Heater Core

So I got the heater core out and found some corrosion on the heater core fins. I decided to try pouring clean water into the core and there was all kinds of crude in there. I also found that after filling the core and capping with my thumbs the tube the water level went down. At least a small leak if not more once under pressure. I am getting a replacement tomorrow Advance has it for 34.99. I also need to replace the heater hoses I had to cut them to get them off.