Lean of peak yep. DONT
When you lean an engine you slow the speed of the of the fuel burn. This means as the exhaust valve is opening instead of the fuel being completely burnt it is now burn out past the valve. Yes im aware of the article but I've seen the results of over peak leaning as many engineers have. Makes money for us. Simple how much fuel do you have to save to replace a $2500 cylinder. Oh and plus the other 5 cylinder's that have to be changed. Even worse if you try it with a turbo engine, added boost can cause a detonation and complete engine failure. Case in point the PA 31-350 in SA while he had an engine failure on one engine he went to a high power setting and didn't increase the mixture as I recall. Now what that means although he didn't intentionally lean to an over peak the result was the same. He then lost the good engine resulting in the loose of the aircraft and all on-board. Yes there lots of other thing that compounded that accident but engine failure stopped the aircraft fly, Was extremely sad.
At the end of the day the exhaust seat and valve don't lie.
So I guess its the owners choice but at the service its the engineers.
This is my personal view and not to be taken as a recommendation. At the end of the day you have to go by what the aircraft flight manual says.
Look owners says this this that, engineer looks sees that that ,this. The machine doesn't lie. Things don't fix them self's.