My '96 Tahoe has developed a leak. I had a "new" (not rebuilt) 4L60E or 4L80E transmission replaced two years ago at 118927 miles. I now have 124670 miles..5743 miles on the new trans. Here is the problem... it only leaks the fluid after it sets, not running. It appears it may be coming out the rear shaft area right in front of the U=joint. There is no sign of fluid leaking from the pan gasket or elsewhere. Although, there is a "slight" sign of trans. fluid coming from the tube. There is no sign that fluid in being thrown out while driving, as there are no fluid on the undercarriage.
I've put three layer of cardboard under the Tahoe to see how much leaks. Sometimes it doesn't leak at all. It looks like it may only be a few spoon full that leak out.
What is the solution here? Remove U-joint assembly and remove the rear transmission part and replace the seal.
There is a rear seal on the transmission. When it's hot, it probably expands a little bit, then as it cools, it shriks and extra fluid leaks out. Did you check the transmission fluid level on the dip stick? If you replace the rear seal, make sure the end of the drive shaft is smooth and dosen't have any rough spots on it that would casue the end seal to wear out.