Reply to "ZF GEAR OIL"

In most cases, the 'additives' are only slip-agents to alleviate chatter in clutch-type LSDs. Lloyd says they don't hurt and may help some ZFs. Chatter is noticable stick/slip in turns, most prevalent on wet or other low-traction surfaces. Many 80W90 diff-lubes already have the right amount mixed in.

If your LSD clutches are badly worn, there will be no chatter. The clutches are easy to check: GM's quick method was to wet down a concrete floor and lay a 2X4 in front of one rear tire. If the car could climb the 2X4 from a dead stop, the LSD clutches were considered usable. There are more precise checks involving a torque wrench on a wheel stud, specific to some LSDs.