"W46 started to overheat. Removed thermostat and found bottow plugged with brown sludge. Wiped adjacent orifices with a rag and got more sludge, but not the big glob found on the thermostat. Would like to clean and flush cooling system, but Parts Manual shows only 2 brass 1/8" NPT plugs located on both side of forward end on engine. Both plugs are virtually inaccessible. How do I drain the block & transmission and flush the system to get all the cleaning agent out and new anti-freeze back in?"