It took 3 years, 100 denim quilts, 3 Project Linus Quilts and 3 Crazy Quilts, but I finally killed my Brother CS6000i. (!!!)
I took it to a local Sew/Vac shop guy who said " I wouldn't touch it."
Looked on line for a Brother Repair shop, who was happy to work on it, but at $120. plus parts, if needed, I said Thanks but No Thanks. The problem it is that when sewing all those denim quilts, I allowed the quilts to "pull" the needle to the left, thus mis-aligning the mechanism.
I HIGHLY RECOMMEND the Brother CS6000i for normal sewing. It only weighs 13 pounds, so GO FOR IT!