I had mine serviced at the dealer as it is under warranty. They had to pull the transmission out and perform a "tear down" to fix it. So, I would assume that if you wish to service the transmission yourself that you will have to remove it.

Here is some info I found that I thought may be helpful for some of you:

The following link provides an illustration and a company who has a fix for the valve problem:
http://www.transmissionspecialty.com.../84754-34K.htm

Here are some instructions out of the technical manual on how to remove the valve body and start the repair (note; this is for a Grand Prix so it may vary a little)

Valve Body Replacement
Removal Procedure
Tools Required
• J 28467-A Engine Support Fixture
• J 28467-90 Engine Support Adapter
• J 36462 Engine Support Adapter Leg Set

Disconnect the battery ground (negative) cable. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical.
Remove the throttle body air inlet duct. Refer to Air Cleaner Assembly Replacement in Engine Controls.
Install the J 28467-A .
Install the J 28467-90 .
Install the J 36462 .
Remove the engine mount struts. Refer to Engine Mount Strut Replacement and Engine Mount Strut Replacement in Engine Mechanical.
Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
Remove the left front wheel. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
Remove the left engine splash shield. Refer to Splash Shield Replacement - Engine Body Front End.
Remove the stabilizer shaft brackets from the lower control arms. Refer to Stabilizer Shaft Link Replacement in Front Suspension.
Remove the left tie rod end from the steering knuckle. Refer to Steering Knuckle Replacement in Front Suspension.
Remove the wheel speed sensor harness connector. Refer to Wheel Speed Sensor Replacement in ABS.
Remove the left lower ball joint from the left lower control arm. Refer to Steering Knuckle Replacement in Front Suspension.
Disconnect the left drive axle from the transaxle. Refer to Wheel Drive Shaft Replacement in Drive Axle.
Secure the drive axle to the steering knuckle/strut.

Caution: Failure to disconnect the intermediate shaft from the rack and pinion stub shaft can result in damage to the steering gear and/or damage to the intermediate shaft. This damage may cause loss of steering control which could result in personal injury.

Remove the pinch bolt at the intermediate steering shaft. Refer to Intermediate Steering Shaft Replacement in Steering Wheel and Column .
Remove the intermediate shaft from the steering gear. Refer to Intermediate Steering Shaft Replacement in Steering Wheel and Column.
Disconnect the three-way catalytic converter pipe to the right (rear) exhaust manifold. Refer to Catalytic Converter Replacement in Engine Exhaust.
Support the right side of the frame with jackstands.
Support the left side of the frame with jackstands.
Remove the transaxle mount bracket. Refer to Automatic Transmission Mount Bracket Replacement .
Remove the transaxle mount. Refer to Automatic Transmission Mount Replacement .
Remove the engine mount lower nuts. Refer to Engine Mount Replacement in Engine Mechanical.
Loosen the right side frame to body bolts. Refer to Frame Removal in Frame and Underbody.
Remove the left side frame to body bolts. Refer to Frame Removal in Frame and Underbody.
Adjust the jackstand to the lower left side of the frame.
Position the drain pan under the transaxle.
Remove the wiring harness connector.
Remove the case side cover bolts (56-58
Remove the case side cover pan (53).
Remove the case side cover gasket (54).
Remove the oil pump. Refer to Oil Pump
Remove the valve body bolts (374-381 and 384).
Remove the valve body (300) while keeping the spacer plate (370) with the transaxle.
Remove the ball check valves (372 and 373) from the valve body.
Remove the spacer plate (370) and gasket.
Remove the ball check valves (372) from the case cover.
Inspect each check valve seat in the spacer plate (370) for excessive peening. Place a ball check valve (372) on each seat and use a flashlight in order to look for visible light between the valve and the seat.
Inspect all components removed from the transaxle. Refer to the Transmission/Transaxle/Transfer Case Unit Repair Manual.