I would second the no additive for the first few thousand miles post. There must be friction during the break-in process. I am a licensed aircraft and power plant mechanic, among other things. A rebuilt airplane engine has about 25 hours, at the most, to break in. The procedure used for years was to use non-detergent oil for the first 25 hours or so. In addition, the best break-in procedure that I have had success with was prescribed by Chrome Plate Inc., a noted engine rebuilder of great engines. It was as follows:
*Start the newly rebuilt engine and only run it on the ground to allow a visual inspection for leaks and insure it is ready to be flown.
*When ready to test fly, start the engine and, minimizing taxi time, take off ASAP at full power.
*Climb to a safe altitude remaining low as prudent to keep air density as high as possible and reduce power to 75% for 30 minutes.
*Then "WHIP" the engine with 5 minutes at full power, followed by 5 minutes at 75% power. *Repeat 3 whippings and land.
When I did the above break-in procedure on my rebuilt engines, the temperatures dropped during the whippings. The oil then stayed clean and the engine was broken in.
The secret here is the top ring seal depends on high pressure to push it hard against the cylinder wall and, per Chrome Plate Inc., wear in the rings and bores by making tiny sparks! This must occur before the varnish sets in.
One of the engines I was able to track for over a thousand hours never used oil and would beat like type airplanes in full throttle friendly competition. BTW, an aircraft engine must be able to operate in a test cell at 100% power and, when torn down and measured, be within manufacturing tolerances.