I've considered a flush, but haven't after reading mixed/limited results. Thirty years ago I'd flush a system and run it down the sewer. Not any more. I can change a heater core using the YouTube hack in about an hour for about $75 with minor mess. I guess it's unlikely that the dealer that changed the core the first time or the shop that did the water pump did any flushing. A company called Mishimoto made a kit for Jeeps and put it on YouTube. I put a link in my first post, but it's hung up waiting for approval. There are a couple of other videos of installs in jeeps. They use a remote, spin on filter and splice it into the heater lines. I first looked it up for journeys after seeing a guy's post about a remote oil filter he installed in the heater line of his Ford Ranger for the same kind of heater core issue. He'd already flushed and replaced multiple parts, and was pretty pleased with the filter he'd installed. I've seen installs on diesel pickups, too. Right now would be an ideal time to put something like that in since I've the car torn apart for a new radiator, oil cooler and the new heater core.