The dirty looking oil that drips into the bowl is from the grease in the gearbox. This is food-grade grease which implies it should be safe, although after 35 years I am not sure about that.
The most important maintenance you can do is to get the "carbon motor brushes" replaced. If you can find a firm that will do this, then they will also know about any oiling it needs.
Paul
April 2006
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