Originally Posted by thepolyparrot
I use TriFlow synthetic lubricant - the drip bottle, mostly, but the aerosol version to saturate the inside of a machine and the grease version on any gears that need it.
The liquid evaporates very quickly and leaves PTFE (aka Teflon) behind. It does not yellow and harden and turn into varnish. The grease stays put and it remains a lubricant as long as it's there - it doesn't turn into putty.
Regular sewing machine oil and the Singer lubricant sold for gears are just fine, too. Just don't use 3in1 or WD40 or white lithium grease.
This is good advice. Most of the vintage sewing machine owners/refurbishers are using TriFlow or regular clear sewing machine oil. You will want to clean all the old oil and grease out first, with an oil based penetrant like Liquid Wrench or Kroil, then apply new oil and grease.