Age is about right. The oil hole leads to a chunk of felt that holds the oil. Motor oil is ok, but a bit heavier than what originally went in there. If it hasn't been oiled in a long time, you can over oil it once to saturate the felt, don't keep over oiling it tho, the oil, if it gets onto the windings degrades the insulating varnish. (5W20 would probably work, 3in 1 is a little thin, but was sometimes used for high speed motors, I'd go heavier than that tho.
Be aware that if you disassemble that motor it may never work again, don't ask how I found that out ;P The armature alignment is kinda touchy in those motors....
If it's running slow it probably needs oil, there is no capacator in those, there is a second shading winding, they do sometimes get cooked, but usually the motor dies when that happens.
Other than that, those motors are close to indestructable....
(Probably came off of a fan, they used thousands of them for fan service)