The 6 speed manual transmission in 1989-1996 Corvettes was produced by German automotive components company ZF Industries http://www.zf-group.de/. The Corvette Owners Manual clearly states that this transmission does not need service, but the transmission fluid level should only be checked and kept full. A bit of research confirmed that ZF does not share this recommendation with GM. Instead, ZF recommends that the transmission oil be changed every 30,000 miles.

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The rear axels in C4 Corvettes are from Dana Corporation http://www.dana.com/ GM does not specify a service interval in the owners manual. Dana Corporation makes the following recommendations: 1. If there is any possibility of water contamination the oil needs to be changed immediately.

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