Have to agree here, I'm not buying the experts opinions here. However my own experience may help (For an 04/05 though but same principles) My last GV had an issue, engine oil warning light on a long drive, limped it to destination and filled up with oil and didn't check properly (My bad, I was at work and had to do stuff/be places). 6-12 months later and I'm checking fluids and spot oil in the water bottle, think film on the top. To check it get a bit of kitchen roll and dip it in. If it's got the shiny oil covering then you've got oil in there. As it turns out I had a crack in the block, which was difficult to find/diagnose (Had head off, pressure testing before the garage it was at.. A Chrysler dealership actually spotted the crack in the block itself). So my thinking, check the water yourself, look for anything like the above, take photos if you want and post here we'll all have a look for you (You're in Durham too, dare say I could have a lookie over if you want another GV owners opinion since you're in this region). Sludge in coolant could be somebody in the past using a stop-leak radiator fixer which is notorious for causing sludge and also blocking/restricting water flow which as the other guys say sounds the biggest culprit. I'd say go for another flush, it's relatively easy to do yourself with a hose and popping various hoses in the engine bay off to flush it out to see if you're still getting sludge, it can be pretty stubborn to get rid of, especially as it gets caught in the heater matrix for cabin heater, etc. Good luck and drop me a msg if you do want another local pair of eyes on it!