Oil change on a 191J
Congratulations on your upcoming purchase of 191J. That thing is a tank. It’s a wonderful machine and you’ll enjoy using it tremendously in my opinion. I own a 201 (1941) and 191J (late 50s). The 191J was my mother’s machine and I’m the second owner, but I have no clue as to the provenance of the 201 since it was purchased last year through FB Marketplace.
I’ve never “changed the oil” on any of my machines. I add sewing machine oil to the bobbin case every time I plan to sew for more than an hour, and I have the machine serviced once a year or so. If you consult the booklet your machine will come with, there should be a drawing with instructions informing you where you should add the sewing machine oil.
Good luck with your new purchase.