The whistle on the cab roof is very fragile and particularly vulnerable. There will be a lot of work to be done with the locomotive upside down, so some sort of protection is going to be needed. I just happened to have some blue coloured sticky stuff available, so I've used that to provide some protection.
Something that must be done before any weathering is started is to remove all excess grease and oil from the motor and drive mechanism. If this is not done then at some time in the future all of the carefully applied weathering will take on the same oily, dark appearance. There is a reason for me knowing this.
Upon closer investigation, it is apparent that this model was lubricated by using a spoon . . . . . . .
It must all be removed, and in this case I employed a cocktail stick so that I could get into all the edges, corners and spaces, lifting the wheels and axles out to clean inside the bearing slots and gearwheel teeth.