When I changed my last rear sprocket I noticed cracks at every bolt hole.....I doubt the sprocket would have lasted another ride. This was a Sunstar steel sprocket. I have a Tucker +4 swinger, so the axle is always straight. Maybe a defective sprocket?

 

The sunstars are a bit weak, you should upgrade to a bit more pricey sprocket if your sure you have the right gearing. If you are planning on getting some insane mods, and want a sprocket that will last forever go with sidewinder. Renthal's have worked fine for me, and are right in the upper middle of the price range.