I own a 2012 Millennium, third hand. Second owner used the machine very little if much at all. Most of my initial adjustments were carriage bolt adjustments and a small burr on a rail. The 'S' catch disappeared.
I've been troubleshooting a racing stitch regulator for the last several months. I downloaded the Millennium manual from this site. It differs slightly from the manual I received with the machine.
My racing 'stitch regulator' happened when my power cord drifted between the carriage rails resting on the encoder cable. Tonight we corrected the insulated cord clamp location. Page 58 of the on-line manual.
My machine has a bobbin winder on the machine head. Love it!
Photo 1: a zip tie behind the thread uptake bracket
Photo 2: view of slack from zip tie toward the right rail (stand in the back of the machine)
Photo 3: View of insulated cord clamp. Note it is attached from the bottom and at an angle. This arrangement gave me clearance of the rear right handle.
Photo 4: Close up of insulated cord clamp and clearance from the encoder cord.
I hope this helps.
PS the quilt on the wall is a 1930's estate find. Hand stitched, wonky as all get out but hope the creator whomever she/he may be is happy it was brought to life. :-)