To clear up oil marks, I pour on regular sugared Coke and let it dry. The follow with either the purple stuff or simple green. Works like a champ.
That's a good start but won't for-sure stop leaks from getting on the floor. Ask me how I know...
Get a piece of sturdy visqueen and put it under the carpet and cardboard. That will make sure you don't lose your cleaning deposit when you leave that joint.