Radiator gunk - location for flush T? Poking around looking at fluids in my "new to me" Cruiser. Opened the radiator cap to find this: Does this look like normal gunk build-up, or stop-leak stuff? My engine's not overheating (even on 90* days w. AC on), and the thermostat was replaced in the past 2 years, so it's not indicating a major blockage. Plan to flush system and replenish with Prestone 5/150 "Extended Life" coolant, probably also drop in some Water Wetter while I'm at it, but wondering if there's something I need to do to get rid of this nasty-looking deposit.