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Oil for rear axle?

Steve--

I do not pretend to understand the technical difference between GL4 and GL5 oils but do know that differentials place tremendous loads upon lubricants which is why you will see words such as "Extreme Pressure" etc. in differential oil names, etc. I'm sure someone else will chime in but since there is no yellow metal in your diff there is no reason NOT to use a GL5 oil which is designed for differentials, not transmissions. The 80/90 refers to viscosity, not the oil molecules' resistance to shearing forces, and that--"High Pressure" or "Extreme Pressure" tolerance is what you are after.
 
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