Don't use racing
oil. Don't use additives. Don't use a viscosity higher than necessary to give you the pressure you desire. There is a pretty good chance that the major
oil companies know what they're doing.
Although I have no proof, I would be very afraid of putting Dextron into my crankcase to remove sludge I probably don't have. When I was a kid (the 50s) the guy that owned the "filling station" near our house would use kerosene to clean out engines. I change my Mobil1 once a year, Last time I looked at the inside of the valve covers they had no sludge whatsoever.
Bob