A brush dampened in the appropriate thinners to clean off the paint at the edges unevenly should work, too. Then add a coupe of dabs of slightly darker "wet mud" coloured paint, lightly & irregularly to roughly simulate the patches in the picture.
To simulate that second type of dusting (on the green machine) I use heavily thinned paint dabbed on lightly with a fine-ish brush, using capillary motion to spread it over the edges where it builds up. This is usually a multi-pass process, so don't expect it to look perfect first time (works better on matt surfaces).**
[**: I use a version of this process around bolt heads, etc, too.]