Janome Overlocker 9200D

Question

Hi Bought from John Lewis 5 months ago, located in my sewing room next to Janome sewing machine. The cutting blade and lower loop and a few other parts around the needle have what i can only described as rust on them. Used daily, went on holiday for 1 week came back to find rust and metal discolouration. Oiled - de fluffed and cared for on a regular basis with correct machine oil. Have taken back to shop and there only line is it has got damp. The wedding dress (current job placed next to overlocker) and the sewing machine do not show any signs of any water damage and the room is not damp. Have you ever experienced this.help