time for a new one. makes me think lead from using 100ll also.
I also want to point out that I used my old cooler, but, I also used my flushing machine, you say what? I own a transmission shop, I have some pretty cool stuff. My machine allows heated trans fluid to flow through the cooler and blast with air the cooler clean, there is a racing filter that is in line and when that is clean, so is the cooler.
The solvent trick is old school. Don't feel bad about the material in the cooler and wasting your time looking for it. Now you know. You can now go out and buy a new one and feel good about doing it.