as mentioned above, vintage/antique motors used mostly oil for lubrication
the motor you have shown is modern enough to have had grease packed in the bearings, hence the end grease cap .
you can safely use a lithium soap or a lithium complex grease in your motor.
many manufacturers make the greases- Sta-Lube, Mobil, Shell, Phillips, Super-Tech (a Walmart brand), Traveller (a Tractor Supply Co. brand), Kendall, Valvoline, etc
lithium complex greases can take higher pressures and heat than the soap counterpart, but both would be acceptable regardless.
another thing to remember, you do not want to overfill a bearing, doing so will adversely affect the operation and longevity of the bearing.
there is a formula for the filling of a bearing believe it or not:
G = 0.114 x D x B
G= grease (in ounces)
D= bore diameter (in inches)
B=bearing width (in inches)