GM Service Manual Online
For 1990-2009 cars only

If the transmission oil cooler has developed a leak allowing engine coolant to enter the transmission, perform the following:

  1. Disassemble the transmission.
  2. Replace all of the rubber type seals. The coolant will attack the seal material which will cause leakage.
  3. Replace the composition-faced clutch plate assemblies. The facing material may separate from the steel center portion.
  4. Replace all of the washers.
  5. Replace the torque converter.
  6. Thoroughly clean and rebuild the transmission, using new gaskets and filter.
  7. Flush the cooler lines after the transmission cooler has been properly repaired or replaced.