Just a bit of information I have collected over the years, if I may.
I don't know if "3-in-1" oil is improved over what it used to be, but
ten years ago or so it still had the problem of turning to gum from
oxidation.

I used to repair record changers, turntables and reel-to-reel tape
recorders, as well as the occasional reel-to-reel video recorder.
I found that Singer Sewing Machine oil was an excellent lubricant which
did not gum, and is readily available.

This is intended for sewing machine motors, as well as the internal
parts of the sewing machine.  It holds up to high temperature well and
stays where it is put, if used sparingly.  I have not had a problem
with Singer oil in thirty years of use, and as such I can recommend it
without reservations.

Jim Cook

 [ For many years I used oil bought at a military surplus store,
 [ produced to Mil Specs for lubricating the motor and shafts in
 [ the Teletype(tm) teleprinters of the 1920s to 1970s.  Military
 [ communications centers operated these machines 24 hours a day.
 [ The oil seemed very similar to sewing machine oil except slightly
 [ thicker.   -- Robbie