Slip means how fast it takes the motor to come up to speed High slip motors like the Sterling M-5 start slower and come up slower there for having less current draw on the line voltage. In the early 20th century Rural Electirc companys Did not have a lot of Electric capacity to work with. The REA also would not alow Motors bigger the 5HP accross the lines.
As a rule you usally do not paint Allumim Rotors. Besides to get this one off would take a act of God. has 1 set screw Rusted and IT would break for sure meaning fun getting the rest out. ANd no puller holes meaning real fun trying to get the rotor off. It was done 3 times in the 80's. i'd love to know how they did it too.