One modification I made was to drill a small hole in the inside rear of the case to allow oil to enter and lubricate the #9 thrust washer. This is a common failure on the C4 and this hole is present from the factory on the C5. Details about this modification can be found here. I used a hand drill and checked my progress frequently. One thing you don't want to do is break through the backside of the case. I made a line from the center of the large opening in the center to the small hole to the left of the hole I drilled and centered it where the thrust washer rides. I just barely caught the side of the oil galley that is molded into the case and I could have started the hole a little bit closer to the top of the case. Make your measurements carefully since you only get one shot at this! Next –––>

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