This question is about the Disco, but it's a 4.0 Bosch. I've been adding about a pint of coolant a week, and I don't drive it a lot. It has 165,000km, and as far as I can tell, the HG's have never been done, so I guessed it was time. I removed the heads, and I was hoping to see more definite evidence of bad HG's. I'll try to post photos again. Also, are #6 liner there is a slight brown streak, but liners all look intact, and slightly below flush.