I would like to change the fluids in my differentials and transfer case - but not quite sure if synthetics are the way to go. Mine is a 93 Cherokee with QuadraTrac and 186,000 miles. Not sure when - or even if - the fluids have been changed. The vehicle appears to have had excellent care - just not sure if the former owner even knew what to do and when. Any advice will be appreciated. Thank You. Jeff