I'm getting to the end of the +15 hour RMI-25 cleaning cycle in the Lumina. I noticed that the filler neck of the radiator has a nice coating of oily/greasy brown stuff that is not water soluble. I'm sure this stuff is only in the filler neck/side tank and in the plastic coolant recovery bottle. I had to change the water pump a few days ago and the aluminum timing chain cover/water pump housing was spotless when I removed the old pump. I want to run a cleaner before starting with fresh coolant and water but opinions here regarding cleaners run the gamut from Preston flush, Prestone cleaner, Prestone flush+cleaner, Cascade, Simple Green, CLR, acid based stuff, etc. I'm thinking just use simple Prestone flush+cleaner (I don't think they make separate flushes and cleaners anymore). Basically, start with the least harsh chemical and go from there. BTW, I'm also not concerned with the intake gaskets. They're not OEM and this car did not have Dex-Cool as factory fill.