I have had only one engine doing what the OP is having a problem with. In my case the fuel tank is mounted way too far back in the fuse and as soon as it burns off about 1/4 of a tank of fuel there isn't enough pressure to help the fuel flow. I thought it was a cracked line in the tank so that was the first thing I looked at. The tank is fine and it's not sucking air. With the tank pulled out and taped onto the fuse closer to teh engine all is fine. That's just something else to look at.
Chrome peeling was a problem with the FX when it first hit the market. That was the number one small engine being used at my field when it came out and it was happening to pretty much all of them. OS got the word and fixed the problem. This is the first time I have heard of it happening with the AX though. I would go into the engine forum right away and talk to Bill Baxter about it, the OS service rep. I don't know if something like lean running over time would do that??After a couple of years you may be out of luck but Bill may want to see the engine and see if there was a manufracturing problem?? Let hm know the brand and type of fuel you have used too. As much info as you can give will help. As for other engines, I have tried the SK line of engines from Kangke and like them as well as OS. I have only tried the .91 though so can't say anything about there other sizes. The .91 is about $100.00 with muffler. As far as two strokes go it's a lot of bang for the buck.