Transmission leaking oil. on 2001 GMC Sonoma

Transmission leaks oil from somewhere unseen on top of the case. It only does it after parked for several hours. The front and rear seals are Not leaking. Overnight it can lose up to a half quart of oil.

Asked by for the 2001 GMC Sonoma
Any chance the trans is overfilled? You need to check the fluid with the engine running in PARK with the engine completely warmed up after being driven. If you overfill it it will leak out the top vent tube.
Nope. I always drive around the block first after warming the vehicle up. As far as I can tell the vent is a hose that runs up the firewall with the actual vent by the trans dipstick at the top of the motor.