These coolers have very narrow passages and can't be reliably flushed, if the donor truck has had a trans failure the crud would have been pumped into the cooler and it will be partially blocked. Always best to start with a new one so you know what you are getting.These coolers are hard to find online for under $100. I will try my luck at finding one at pik n pull tonorrow. My truck has the stock trans cooler, so thats a relief!