I sent mine in for that. I knew there was something off right away in servo mode. No reason that camera can't track a steady BIF (even if it is fast) using factory settings and be consistent during bursts. I set it up like my 7D which did not have case numbers. I used case 2 with TS set to -2. That has no real effect on initial AF acquisition or tracking anyway, just how it reacts if your all your AF points go off target. When you achieve focus and keep your points on it should be consistent. Shot that way for 5 years with my 7D.
I got lucky. New Jersey did a good job. A member at Fred Miranda had the same issues and NJ was waiting for a special tool from Japan. I waited until they got it before I sent mine in and was very specific in my service request. I have always had good service from NJ.
I sent mine to New Jersey three times. Mine had been perfect for ten months then started producing mush. They ended up sending me a new one that I never used. I was getting great results with my 1D IV.