Murphy's contains neither oil nor soap and they will not divulge all the ingredients. So, that cleaner may not ruin your existing finish but the problem is when it comes time to have a maintenance recoat performed. If the existing finish is polluted by the Murphy's cleaner, then the new top coat will not bond or perform properly. Most major finish manufacturer's warn against using "oil soaps" as cleaners. There are generic wood floors cleaners for urethane finished floors in most hardware stores. My favorite is Bona Hardwood Floor Cleaner available in flooring supply distributors and many retail flooring outlets. Did you read this?
http://www.hardwoodinstaller.com/hardwo ... orcare.htm