Any suggestions? They are really bad. The rest of the sofa is ok and clean as the covers are removable and washable, but the arms have never been cleaned. The dirt/stains are very worn in now (I did make washable arm covers which hide it well so not a total slob), but we have no idea what to clean it with. Is this a case for bi-carb? If so, how do we go about it and if not, what should we use? Do I need to go product hunting? HELP please.