Is surface rust covered by Triton warranty?

We have two questions relating to our 2012 Mitsubishi Triton. We have electronic rust protection and have noticed some surface rust appearing. Is this normal or covered with warranty? And we had our clutch fail yesterday and told today it's the slave cylinder and that it's not covered under warranty as sand got in and cause a leak. We still have almost a year on our warranty and I thought driving the car for what it's designed for, would be covered by warranty. We do go up the beach about four times a year. It always gets a thorough wash and clean after use.