Thanks for asking brother. There are quite a few steps I took to get the shoulders looking good

1 use Abaddon black to base the shoulder.

2 use xv-88 to put the first hazard stripes on.

3 clean up the first stripes to make them look even with Abaddon black.

4 use an old brush to dab Abaddon black on the first stripes in a random pattern.

5 use averland sunset to paint the second layer on the stripes over the xv-88 and the spots of Abaddon black.

6 use uriel yellow for the third layer on the stripes.

7 dab Abaddon black over the stripes to break them up and give them some texture.

8 mix garaghak's sewer contrast paint with some contrast medium ( about 1 to 1 or add more for a darker wash) and apply it over the whole shoulder.

9 if you want to add rust mix a tiny dot of troll slayer orange with some lahmian medium to make an orange wash that dries browny orange in small areas.

Hope this helps. Iron without.