I thought of one other thing that you should check out. As you know oil gets pumped up to the top end of the motor and gets directed towards key frictional components, namely the working guts of the cam and valve assemblies. However the oil must flow back to the oil pan by simple gravity feed down through the casting holes in the heads. In severely sludged motors these drain holes can become plugged or severely restricted. In the perfect flow situation for every quart of oil pumped up to the top end of the motor, in the same time a quart should be draining back down.
To check this out take a dip stick reading after the car has sat overnight and remember the spot on the dip stick. Then start the motor up and allow it to warm up for five minutes or so, giving it some slight revs along the way. Shut the motor off and check the dip stick again within 30 to 45 seconds after shut down and see if it as the original level. It certainly should be in a minutes time. If not, then it is highly likely that you have some blockage. Auto-Rx can not clean where oil can not flow.
One other thing to check out is to be sure that your head gasket is sealing properly. Check for signs of oil in the coolant.
In some situations where the size of the drainback holes is too small, coupled with an engine design that tends to form sludge, such as the 3 liter Toyota V6's, you may have to go in and physically clean these oil drainback holes. Once a hole is plugged shut with sludge, there is no flow where Auto-Rx can get down through there to clean it up. That was my experience on 2 different engines.
