I finished it off with oil paints and Copic sketch markers which act like brushes. I used the Copic blending marker as well as Tamiya thinner to get the results I wanted. The Tamiya acrylic thinner is alcohol base, so it works well with the the Copic markers which are alcohol base too. In his first book, Kow Sensei uses the markers on a Schenkel and Snakeye for weathering and shading.
In this entry, For Struschie. Painting a Mel as in the picture below it, you can see how I pre-weather the model with oil and lacquer paints.
And in this entry, MEL VARIANT after the decals, I started to use Copic markers for rust and streaking and oil paints for colour modulation resulting in the final weathering on for the Mel.
One last thing. Well two:
1. I cut the PKA exhaust down at the pipe's return enabling me to mount it closer to the engine cover. I also turned it pointing downward. The way I originally had it; pointed up and further away from the engine was irritating. Now it counters the other surface details that are mounted in an upward pointing position. It makes the silhouette of the Mel Variant cohesive now.
2. I'll have more pics (studio quality) at some point... in case you care. :)
3. Thanks you Struschie for the engine cover!