I don't know what kind of needles to use. I have three older machines (117.552 158.18030 158.13201) all bought used. The manuals all say use Kenmore needles -not enough info. Is the 15x1 series of needle right for these machines made between 1940 and 1980?

You can use Kenmore, Singer, Klasse, Schmetz or Organ needles for home sewing machines - they are the same configuration.

The instruction manual should indicate how to insert the needle, either according to the flat side of the needle shaft or the groove down the front of the needle.

Needles for older machines may require a round shaft needle. Needles for industrial sewing machines have a round shaft.