I know this isn't a leather machine but I gotta tell you folks. About a year ago my daughter, who likes to make stuffed animals, was using it and it started missing stitches and hanging up. Well I had another old singer 401a that I was given and cleaned it up for her to use. This week after making masks all week I decided to try my luck at fixing the problem with the Kenmore as it is a free arm and is useful for clothing repair. Well I have literally taken that darn thing apart 20 times cleaned every inch of it, oiled it, watched every d%^n youtube video on timing issues and basically pulled all my hair out with no real luck. I switched bobbins, needles, hook assemblies, timed it , re timed it and still it would miss a stitch and hang up once in a while with no real reason sometimes four or five times in a row. After THREE friggin days and a spool of thread I figured it out!!!! I noticed the plate that the needle goes through had been hit with bent needles and damaged to the point the burrs were catching the thread randomly and causing the missed stitches, filed it up nice a nd smooth and runs like new!!!!! Hopefully this info may help someone out as I would think leather machines could suffer the same problem.