Be carefull not to over tension the chain. This could of happened by accident some time back. This is when crack likely started. It will always start to crack at a weld. I've replaced a few augers over the years and often times I have to loosen the chain to hook up the connecter. Worn sprockets make this even easier to happen. A guy snugs the chain so he can just slide on sprocket then when he puts it under load the chain runs up on the worn area. When the chain runs up on worn area it severely overtentions which keeps the auger bowed and bending every revolution. Eventially it will break near a weld. When I tention a chain against worn sprockets I will turn auger to get chain up on worn area. This will prevent overtension while under load. Good luck
