When you first purchase a new Leimbach pump they look like this.
The oval hole closest to the motor is just to tighten the drive coupling to the motor shaft and the set screw next to it, is to fasten the motor to the pump.
We all know that after long usage the pump shaft seals begin to leak and the oil can carry over to the motor with this result.
Sorry for the quality of the picture but i think you can see that the brush holder is just a big gob of gooey oil and carbon dust. It took an hour to take the motor apart and clean it out and reassemble it,
The reason I have shown the first picture is if you loosen the setscrew and turn the motor one half turn now you have a place for the leaking oil to drain out of and it will not carry on to the motor
This motor was so bad that there was 3/4 of an amp leaking to the case of the motor and it was a smoke show and it would get so hot you couldn't even touch it. After it was cleaned it runs as cool as ever.
Rob