I spent some time pressure flushing the core with the hose, back and forth untill it ran clear, then I filled it with some radiator flush solution and left it for a few days.
More junk came out, so another power flush and it seems to be clean inside now.
I retested the pressure, just in case.
Here is my pressure test rig!
Two Short lengths of 3/8" hose, 4 hose clips, one old tire valve, and one bolt with a round caphead, that was about 3/8" dia.
Looks like this assembled...
I know that the radiator system cap can be 12 or 16psi, and my Craftsman coolant pressure test kit says 25psi is the maximum safe pressure, so thats what I tested it too.
I pressurized the tire valve to 25psi via my tire inflator, from my compressor.
I tried it in a bucket of water... but there is so much air trapped in the core vanes, it was still releasing bubbles forever after!
In the end, I left it out of water for a couple of hours, and then rechecked the pressure, and it was within 1psi, which allowing for the small volume of air and the slight loss every time you attach and detach the inflator.
I think I will call it good!
Time to reassembel the unit!