1974 Other Chevrolet Models leaking 350 turbo transmission

If it was rebuilt by a reputable place they should take care of it. Alot of times the pan is torqued to tight and causes this. There is a shifter shaft seal but it normally doesn't leak like that. I'd check the govenor cover, or the servo on the passenger side or actually take the pan off and get a new gasket and only torque the bolts at about 10 ft. Lbs no more. Also check your lines for leakage as they have steady pressure when ever the engine is running and that's where they leak often.