Here are some things to look for when looking for the fluid leak;
Fluid leaking by the front pump seal lip will tend to move along the impeller hub and onto the back of the impeller housing. Except in the case of a total seal failure, fluid leakage by the lip of the seal will be deposited on the inside of the torque converter housing only, near the outside diameter of the housing.
Fluid leakage by the outside diameter of the front pump seal and front pump body will follow the same path that leaks by the inside diameter of the front pump seal follow.
Fluid that leaks by a front pump to case bolt or pump gasket will be deposited on the inside of the torque converter housing only. Fluid will not be deposited on the back of the torque converter.
Fluid leakage from the converter drain plug, converter seal weld or converter to flexplate stud weld will appear at the outside diameter of the torque converter, on the back face of the flexplate, and in the converter housing only near the flexplate. Fluid leaks from the torque converter will leave a ring of fluid around the inside of the torque converter housing.
NOTE: White facial tissue may aid in determining the color (red is transmission fluid) and source of the leaking fluid.
Engine oil leaks are sometimes incorrectly diagnosed as transmission pump gasket leaks. The following areas of possible leakage should also be checked to determine if engine oil leakage is causing the concern.
Leakage at the valve cover gasket may allow oil to flow over the torque converter housing, or seep down between the torque converter housing and cylinder block, causing oil to be present in or at the bottom of the torque converter housing.
Oil galley plug leaks will allow oil to flow down the rear face of the cylinder block to the bottom of the torque converter housing.
Leakage at the crankshaft rear oil seal will work back to the flexplate, and then into the torque converter housing.
Leakage at oil pressure sensor.
Leak Check Test
Determine the cause of the leakage before repair.
Remove the fluid level indicator and note the color of the fluid. Original factory fill fluid is dyed red to aid in determining if leakage is from the engine or transmission. The red color should assist in pinpointing the leak.
Remove the torque converter housing cover. Clean off any fluid from the top and bottom of the torque converter housing, front of the case, and rear face of the engine and oil pan. Clean the torque converter area by washing with a suitable non-flammable solvent, and blow dry with compressed air.
Wash out the torque converter housing, the front of the flexplate and the converter drain plug. The torque converter housing may be washed out using clean solvent and a squirt-type oil can. Blow-dry all washed areas with compressed air.
Start and run the engine until the transmission reaches its normal operating temperature. Observe the back of the cylinder block and top of the torque converter housing for evidence of fluid leakage. Raise the vehicle on a hoist and run the engine at fast idle, then at engine idle, occasionally shifting to the Overdrive and Reverse ranges to increase pressure within the transmission. Observe the front of the flexplate, back of the cylinder block (in as far as possible), and inside the torque converter housing and front of the case. Run the engine until fluid leakage is evident and the probable source of leakage can be determined. When a converter drain plug leaks, remove drain plug and discard. Install a new drain plug and tighten plug to 26 Nm (19 lb-ft).