1-2-3-4 Clutch
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The 1234 clutch fluid enters the 1234 clutch housing to move the piston against spring force and compensator feed fluid to apply the 1-2-3-4 clutch plates.