I recently got a 401A as you know and found that mine was also slightly off (set @ 8 and stitched 10....all fixed now). Can be a hard one to pin down if you haven't recently adjusted anything. From my experience, stitch length issues are always from adjustment issues or could simply need a deep clean inside where feed fork connecting rod is located (especially around the slide block area). Apologies, not much help but nothing serious in my opinion also.....Just a matter of setting the machine up correctly, not forgetting that deep clean...some peeps forget or miss this area when cleaning out old machines
