How do I add differential oil to the front and rear differentials? I was told I need a special tool due to space restrictions... Also what is the best lubricant to use? Is this ok Differential / Axle...

2006 Full Size RR SC 4.2L. 140K Coolant level low light came on over the last few weeks. Never overheating, thermostat gauge always dead center. Bought a gallon at RR dealer yesterday. Made 2 gallons diluting with distilled water. Figured rather than just top off why not drain a...