Joe, if you're gonna open it up anyway, swap the guts from another motor. That way you keep this motor case matching the machine.
I'm suspecting the pressure foot pressure spring as the culprit here for the feed issue. I have a clone that does not like to sew two pieces of fabric in a straight even line, but for free motion work she does great. Her pressure spring is worn out and can't put enough pressure on the fabric for it to feed properly, but put a quilt sandwich under the foot and she's off and running, beautiful stitches as long as I'm guiding the motion of the fabric.
Cari