I agree with using the AutoRX. It is a metal cleaner originally created for printing presses and adapted to automotive use. It will not harm your engine. In my experience, and that of many other users, it performs as promised.
I first used it last December, and continue to use it in maintenance doses. Since my engine was already very clean, I did not experience dramatic results, other than the oil dipstick becoming cleaner and shinier (which suggests the metal parts of the engine are also cleaner and shinier).
Your dirty oil does not necessarily mean a dirty/sludged engine. All the dirt and contaminants may simply be suspened in the oil, as they are supposed to be. If you are concerned, remove the valve cover and have a look. (Even looking under the oil filler cap, to see how silvery the metal parts are, will give you some idea of overall engine cleanliness.)
Frequent oil changes (say 1,500-2,000 mile intervals) with Mobil Delvac, Castrol Tection, or some other 15W40 diesel oil will clean the engine quite well. (Your 30-minute job did nothing.) After that, use AutoRX if you want additional assurance, or for general maintenance.
You are correct to use the lowest
feasible viscosity, to make sure the oil flows as freely and thoroughly into every nook and cranny. In the heat of the summer, that means a 40-weight, and Shell Rotella 5W-40 is great if it does not get too hot where you are. Otherwise, you can't go wrong with Castrol 10W-40.
In the winter, 10W-30 will do just fine.