quick question. i purchased 75-140 royal purple gear oil for the rear diff and picked up the additive from mopar. on the bottle of the oil it says "do not use in wet clutch systems." and the Lucas oil i purchased for the front (75-90) says no additive needed. my question is do i put the mopar additive in the rear with the royal purple and does the front require additive as well. i'm just nervous cause i do not want to mess anything up.