Why did Scythe Master put lube on Ein?
It is symbolic.  In this scene, he is cleaning his weapons.  In Gusseppie's mind, Ein is not human, she is a weapon.  An inanimate object, and in the same way he cares for is ruger, he cares for Ein.  While I don't think he was literally rubbing her down in weapons lubricant or copper solvent, I believe the intent was the same.