Okay, I just got home. Whew! There's a lot to say here. Firstly, to the person who asked, Yes, I did use fresh non-ethanol gas. Okay, I showed up late with not much time to hash things out because I had to be to work. I got a late start out of the driveway. When I got there I saw the saw and could tell immediately that it does need a new top end. The piston was scored badly and shavings of it had adhered themselves to the inside of the cylinder. Looks just like the pictures Marshy linked to that I didn't see until I got back home just now. The owner still adamantly stressed that it was the oil I used and still holds that you should only run Stihl brand oil. He asked me what temperature it was outside when I started the saw after I added the new mix and I told him it was warm. He was like well there you go. The wrong oil on a hot day will always do that. I told him I just wanted to pick up everything and fix it myself and he got sorely offended and said he would work a deal with me for just shy of $500 to rebuild it as a Christmas gift. I reluctantly told him okay, go ahead. Wait, keep reading. I regret saying that. I believe in either paying the shop out of convenience or paying for the education by doing things myself. I hate paying someone else for something I know I can do myself. You've all been there. Just the other day I had to pay a shop to put a new master cylinder in my wife's van. I don't have the time. I hate that. So, because I don't have a ton of free time and $500, I thought, is much more realistic and I needed the saw asap I said go ahead. Then, I found out what they did with my MS250 I left for them to put a new chain sprocket on. They told me $150 for that. And I'm like, why? I just wanted a sprocket and a once over and they said they rebuilt the carb, replaced the plug, filters and all. Okay that's it. The 250 was running like a top already. If the carb needed rebuilt why didn't you ask me first. By that time I realized how late it had gotten so I had to leave in a hurry to be to work on time. So, I haven't picked up anything yet or paid them any money. Hopefully they haven't started work on the 660 yet because I changed my mind. I've decided I'm going back tomorrow morning to pay them for the 250 and pick up my 660 in pieces and pay them whatever they're charging for the diagnosis and do it all myself when I get time. The owner really ticked me off me too when he told me I would mess it up by doing it myself.