I sew on a 778 regularly. Mine is a work horse. I LOVE It. It needs lots of oil , especially in bobbin area. Oil attracts lint. I clean mine with every bobbin change with a pipe cleaner. Also be sure to cut any thread from starting to wind off. That can cause noise and not work. I have not had it commercially serviced in 5 years. Any little bit of lint or 1/8 inch of thread caught somewhere will cause improper stitching. The only 2 replacements have been the feed dogs, original rubber to metal and foot pedal. Also regularly changing needles helps. I use that machine for an average of 5 hrs daily.