The running gear is only beginning to show the grime attracted by the excess lubricant where moving metal components are in contact. It is difficult to fully appreciate the amount of detail weathering without seeing the model in person. On the boiler for example, all raised surfaces such as boiler bands, steps and sander valve hatches have had their edges highlighted to simulate the grime that is typically 'caught' by those edges while on the road. By comparison, making everything look dirty and used is easy!