Yup. What she said.
Sometimes the lube on the gears congeals. You may need to scrape that off and apply new lubrication. (Lube is not the same as oil; it is thick and comes in a tube.) However, that would probably be the last thing you would try.
With older machines I take out any screws that are holding the top on so I can see the moving parts, and oil all of the moving parts (just one or two drops of oil at each spot). Usually the left side can be opened so you can also oil all of the moving parts in there. Sometimes it's possible to take the bottom off and oil those moving parts also.
Once you are pretty sure you have oiled all of the moving parts you can see, it's a good idea to "burn in" the oil by running the machine at full speed for 1 to 3 minutes. Be sure to remove the needle before doing this! It helps get the oil distributed.
Does this machine have an exterior belt? Sometimes those are loose, and sometimes the motors that run those belts have worn brushes inside. These problems can be fixed at home, but it helps to have some knowledge of mechanics and motors.
Usually the older machines are not worth taking in to a repairman because of repair costs. I routinely buy old working machines in thrift shops for $30 max, which is much less than what a repair shop around here would charge for cleaning, oiling, and minor repairs. That's why I do all of that myself. (I donate the machines to a local charity.)