Before you just want to get as much oil out of the radiator as possible, as well as out of the hoses and lines. When you change the cooler dont fill the system back up until the truck is running again. Your going to do more flushing after it's running with a new cooler. You will fill it with purple power and water or something similar and flush it out over and over until its running clear.

The ecm should be fine, if anything add a zip tie to keep the plug in place. They probably broke it trying to diagnose the problem before deciding to auction the truck. I'll pm you in a bit.