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This subject has probably been flogged to death, but I need your comments. Here in Canada, the GM 75W-90 gear oil costs C$30.00 per litre (near enough a US Quart). It complies with this mysterious GM specification 9986115 which seems to exclude any other make of oil under the sun. The cost of Castrol, Shell, Mobil 1 etc synthetic GL-5 75W-90 is about C$12.50. Apart from gouging the customer, what is so special about 9986115 that justifies the cost differential.
If I use the non GM oil, will it nullify my warranty if I have problems? What are your recommendations for synthetics for both differentials?
If I use the non GM oil, will it nullify my warranty if I have problems? What are your recommendations for synthetics for both differentials?