Interesting, but not surprising these days.
Funny thing, I only put pistons in 1 that the customer payed for, all others and I'm guessing I'm close to 4 digits in numbers, were on GM's tab.
Carbon on cylinder walls? Where?
The only time I saw actual damage is when people continue to drive with no oil.
Part of it is consumers going 6-7k on interval, nobody checking the actual level and on GM for saving maybe $4 a car by not utilizing an oil level sensor.
That sane engine used in a car, say a Malibu very, very rarely would use oil.
I believe I have only replaced pistons in 4 or 5 cars for consumption. Vehicle weight play a factor?