CHEVROLET 1999 Corvette - Manual (Page 269)

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Change both the fluid and filter every 50,000 miles
(80 000 km) if the vehicle is mainly driven under one of
these conditions:
D In heavy city traffic where the outside temperature
regularly reaches 90
_F (32_C) or higher.
D In hilly or mountainous terrain.
D High performance operation.
If you do not use your vehicle under one of these
conditions, change the fluid and filter every
100,000 miles (166 000 km).
See “Scheduled Maintenance Services” in the Index for
the proper service intervals for the transmission fluid
and filter.
Manual Transmission Fluid
When to Check
A good time to have it checked is when the engine oil is
changed. However, the fluid in your manual
transmission doesn’t require changing.
How to Check
Because this operation can be difficult, you may choose
to have this done at your Chevrolet dealership
Service Department.
If you do it yourself, be sure to follow all the
instructions here, or you could get a false reading.
NOTICE:
Too much or too little fluid can damage your
transmission. Too much can mean that some
of the fluid could come out and fall on hot
exhaust system parts, starting a fire. Be sure
to get an accurate reading if you check your
transmission fluid.
Check the fluid level only when your engine is off, the
vehicle is parked on a level place and the transmission is
cool enough for you to rest your fingers on the
transmission case.