I read in the manual every 8 hours. Realized that meant 8 hours of sewing. In some spots, that seems to be too much.
Oiling the bobbin area, Juki 2101, after 10 hours of sewing, there was a slight puddle of oil in the base.
I had a PQ 1500 and had to do my own repairs after a Brother Dealer cleaned it, and there were oil drips in the chassis.
These machines need a dipstick.
The Pfaff 2170 is sealed, but we were told by the dealer to put a drop of oil on the needlebar and takeup lever, and around the bobbin spindle.