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From: rec.autos.?

MTL

   75W/80W GL-4 A manual transmission/transaxle lubricant. It provides
   a low temp. shiftability equal to an ATF but will not thin or sheer at
   high temp. Allows faster shifting due to a higher coeff. of friction.

MT90

   70W90 GL-4 A SAE 90 version of MTL for those manufactures who
   recommend a SAE90 GL-4 oil. Uses the same chemistry as MTL.

75W90

   Exceeds GL-5 The preferred product for most car differentials.
   Contains friction modifiers for limited slip units. Can be used in MT's
   and transaxles but other Redline products provide better syncronization.

75W90NS and 75W140NS

   GL-5 lubricants which do not contain friction modifiers for
   limited-slip hypoid diffs. This makes the synchronizers to come to speed
   more rapidly, allowing faster shifting.

80W140

   Exceeds GL-5 Can be used in transmissions where noise is a
   problem and in limited-slip diffs. which vibrate when cornering.

Lightweight Gear Oil

   75W/80W GL-5 For transaxles which recommend 80W
   GL-5. Excellent low temp. flow and good syncro. compatibility. May be used
   in racing diffs. that do not see high temps.

Super Lightweight Gear Oil

   70W/75W GL-5 Use for race qualifying laps.