It would be smart to take it apart and inspect it. Is the commutator round and not worn too much, are the bearings clean and good, are the brushes good, and does the wiring look good. You never know who has down what to a generator of the years.
If you do not have special tooling and understand electronics, it is would be best to send it off to a reputable generator guy.
Once done you would likely only ever need to oil it for the next 50 years or so.