I have a feeling that the law on deposits changed a fair few years ago such that it's a lot harder now for deposits to be retained by landlords over piffling things. Even when they did that, a friend rented a place for only a short while yet they claimed an oil spill on the drive (that was already there beforehand) and, laughably, dirt on the inside of an airbrick vent. The friend successfully took them to small claims court. Hopefully yours should be plain sailing.
By the way, sugar soap is brilliant for easily removing stubborn dirt and grease. Buy at a hardware store (maybe some pound shops) as a liquid spray or a packet of powder that with water makes 10 Litres, costs about a fiver.