Bulletin No.:

Service Bulletin

Date:

22-NA-173
November, 2023

INFORMATION
Subject:

Information on Transmission Fluid Leak

Brand:

Model:

Chevrolet

Corvette

Model Year:

VIN:

from

to

from

to

2020

2024

—

—

Engine:

Transmission:

All

All

Involved Region or Country

North America, Europe, Israel, Middle East, Japan, Thailand, Australia/New Zealand

Condition

Some customers may comment that transmission fluid can be seen under the vehicle.

Information

The following photos are only for informational purposes and to help guide technicians to
known areas of possible leaks. Testing in the photos used fluorescent dye to aid in better
photography. These transmissions were scrapped after dye was added. At no time should
a technician in the field add dye to the M1L transmission. Technicians should only follow
the trace powder diagnosis procedure recommended in Fluid Leak Diagnosis in the
Service Manual.

Important: Service agents must comply with all
International, Federal, State, Provincial, and/or
Local laws applicable to the activities it performs
under this bulletin, including but not limited to
handling, deploying, preparing, classifying,
packaging, marking, labeling, and shipping
dangerous goods. In the event of a conflict between
the procedures set forth in this bulletin and the
laws that apply to your dealership, you must follow
those applicable laws.

Examples of Transmission Leak Areas of
Concern
When performing a leak test always be sure to clean
the transmission thoroughly prior to powder testing.
Make an attempt to protect the transmission labels from
any type of solvent that may be used. Solvents can
erase the print on the labels and make the transmission
difficult to identify. A great opportunity to recreate the
leak after powder application is to perform the Hydraulic
System Leak Test in service information document
5659563 multiple times until a leak is visible. Because
of the elevated RPMs in this test and the vehicle being
stationary, always monitor engine temperature. If the
coolant temperature is excessive and fans continue to
run it may be necessary to allow the vehicle to cool
before continuing testing.

Copyright 2023 General Motors LLC. All Rights Reserved.

Page 2

November, 2023

Bulletin No.: 22-NA-173

6142752

A leak between sealing plate and Bell Housing.

6142966

Leaks at the gasket area between the clutch and
differential cover and the main case. There is a gasket
in this area.

Bulletin No.: 22-NA-173

November, 2023

Page 3

Video (Oil Leak) (SIO# 6460614)
This video above shows transmission case porosity,
issue during testing.

6142841

This is an area that is often mis-diagnosed as a
transmission cooler issue. It was found that in most
cases, leaks in this area are caused by transmission
case porosity under the transmission cooler. Proper
diagnosis in this area would be to inspect the cooler for
any signs of physical damage. If no damage is found,
carefully remove the cooler, and inspect the two (14)
O-rings for damage and proper sealing. The dye photo
shows a puddle of oil just under the cooler sealing area
in the pocket, the fluid is being pushed through the
case due to material porosity. This concern will require
transmission assembly replacement.

6142814

A small crack in the clutch cover area (1) of the input
shaft seal can be mis-diagnosed as an input shaft seal
leak (3). Additional cases have been verified at the
input shaft end plug/seal (2), was damaged during
transmission to engine mating.

Page 4

November, 2023

Bulletin No.: 22-NA-173

6142818

Porosity concerns with the differential cover. This area
needs to be carefully powder tested to verify the leak is
not associated with the cover seal (16) or the
dog-bones and seals. Technicians have stated that
they have found the cover double-gasketed when they
confused the metal differential shims with what they
thought were gaskets. All shims need to be re-installed
to retain proper bearing load on differential. If porosity
is found in the cover, the transmission will require
replacement.
Note: Due to a revision in service information, the
engine cradle no longer needs to be removed to
replace the auxiliary canister filter housing. This led to
an update in the labor time study and the labor hours
for this repair have been adjusted to reflect this.

6142744

The auxiliary canister filter can create leaks in several
areas. The most common area is cover seal (20),
O-ring installation issues after filter replacement. Other
areas of concern can be found at the are O-rings (12)
and (17).

Note: Inspect the cover prior to replacement of the
seal for porosity issues in the O-ring groove area.

Bulletin No.: 22-NA-173

November, 2023

Page 5

6456550

Transmission rear cover area leak. (Tremec name
plate):
• If there seems to be a leak in this area, be sure to
clean the area thoroughly. Residual oil can get
trapped between the outer surface and the O-ring.
• After powder testing, if a leak re-occurs, remove
the cover, and inspect the O-ring for damage.
• If no obvious damage is found with the O-ring, be
sure to inspect the cover itself for porosity issues
in the O-ring groove. It is critical to identify the
difference between a leak and dampness.

6142979

Transmission case porosity concerns have been found
in the SAV cover area of the transmission. This is often
the most misdiagnosed leak on this transmission. The
fluid seeps through the case and runs down between
the SAV cover and case to the pan rail, and often the
transmission pan, and gasket get replaced, then the
SAV cover, and finally the transmission. Often these

leaks will not develop by just allowing the engine to run.
Usually, the vehicle will need to be lifted safely on a
hoist with the wheels raised to allow the vehicle to run
in gear. This action applies to most porosity leaks.

Page 6

November, 2023

Bulletin No.: 22-NA-173

Version

4

Modified

Released August 24, 2022
Revised June 06, 2023 – Changed Engine and Transmission RPOs to All.
Revised October 16, 2023 – Added the 2024 Model Year and Additional Information
under Examples of Transmission Leak Areas of Concern section.
Revised October 30, 2023 – Added Israel, Japan, Thailand to the Involved Region or
Country section and added a Note above the auxiliary canister filter information in the
Examples of Transmission Leak Areas of Concern section.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a
job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.

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