Well, it sure ran great for awhile. Went through two tanks of gas, it was running better than ever. That was with the new Chinese carb and after de-gunking the piston ring. Then with it running fine I shut it off and later with it cold, it wouldn't fire at all again.
So, turns out the same thing happened again, the piston ring was stuck. I thought I had cleaned out the groove pretty well with a tiny screw driver and I cleaned the ring with steel wool. Yet it's gunked up and stuck again. I think my earlier suspicion, that using that 40 year old can of Stihl two cycle oil is the problem. I know new synthetics are better, but I had that old unopened can and figured it should be OK for a leaf blower. I guess it's not. I think something may happen to the oil over all those years, where it no longer performs like it should Maybe it gets gummy or something.
Bad news is that the piston ring broke on while prying it out. I have a new one on the way. Fortunately I got most of the leaves that had to be done blown, so I can wait a couple days for it to get here from PA. I also found a tiny flat file that I can use to clean the piston groove out much better this time. Last time while I cleaned it and it seemed the ring floated freely again, I know there was still some carbon in there. And I'm going to go get some new two cycle synthetic oil, then hopefully I'll be good to go again.