Hello all. I am new here, but I have learned much by searching the forums. My wife and I just purchased a barely-used Econosew DNU-1541s (Jukie 1541s Clone) in beautiful condition.  My wife is a very experienced sewer, and I am just learning to sew. We recently hired an experienced technician to check over and adjust the machine, as this is our first walking-foot machine.  The technician sold us a replacement "M-size" bobbin case, as the original bobbin case's tension spring was s