I am always puzzled that we don't see this question more often. The two are likely very closely related, sludging and rear main seepage. If you haven't already done so, check out the PCV valve and associated plumbing to be sure it is operational. This could have been the cause of the sludging as well as the leak. Restoring the PCV valve to operationality if this is the case could drastically slow down the leak on its own. Also if the valve is stuck, sludging will likely occur again once we get the motor cleaned up.
I would start out by running a basic application. That is adding a full bottle of Auto-RX to a fresh fill of conventional oil, with a new filter in place. Operate the truck as you normally would for 2500 miles. Also I suggest changing out the filter only at the half way point or roughly 1250 miles. This will prevent the possibility of the filter becoming full and going into the bypass mode. After finishing up the 2500 mile run, drain the oil, change out the filter, and refill with conventional oil. Operate this oil change for 3000 miles. This is the rinse phase and no Auto-Rx is added during the rinse phase.
There is a good possibility that the rear main will be cured or slowed dramatically by the end of this first application. With respect to the top end of the motor, you will have made a good dent in the heavy sludge. At least the key components cam lobes, lifters, rockers, should be cleaned up greatly. Cosmetic areas that see only minor splash fed lubrication will take longer to clean up. My recommendation is to start the second application at this point. It will take two applications minimum to get the top end back to respectability.
Along the way you should get better ring to cylinder bore sealing, preventing a good deal of blow gases slipping past the rings. This will help take some pressure off the PCV system and prevent fuel dilution of the oil. Keep us abreast your progress.
