So, the piston wore out ... but the oil is working just fine ... OK.
IMO, the Asian clones are not as durable as OEM saws. I know of a guy who killed two Asian clones (that I built) in a matter of months running Stihl oil at 50:1. I had run both saws a good deal with Saber W/O any problems.
I built a 3rd saw for the guy (all the same) and told him to run Saber at 40:1. I also built one for his Dad and told him the same thing. They have both run their saws for years w/o any problems. (The Son uses his a lot, the Dad not so much.)
I'm not saying you cannot run a stock saw on Stihl oil for a good amount of time, but I'm pretty sure there are better options out there that will prolong the life of your saws. I also believe running better oil is very important if running ported or AM saws, and especially if it is a ported AM saw. One of my clone 660s makes 8.6 Hp., so I'll stick with the Saber at 40:1.
I think running good oil is especially important since they got rid of leaded gas in many areas. Lead acted as a lubricant. FYI my 10mm 044 still runs great. I purchased a new piston and rings for it, but when I ripped it down (to delete the gasket) I decided to leave the original piston and rings in it. There was nothing wrong with the original piston, and the replacement was not quite the same. The original KS piston has stabilizers and a slightly longer skirt.