If you haven't yet changed the differential fluid, or at least checked to make sure it is full, now would be a good time to drain that and fill with fresh at the same time that you put in the additive.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC