Hi guys,
Ok,so finally I fnished the tracks, I still have a lot of issues with individual links, plus trying to put them with the side panel holders glued was nightmare and the tracks started braking into smaller links!! 
This kits has tons of fitting issues.
OK, so put them on, and added my muddy, slushy recipe...currently is over done, but I will scrap off some of it to level it ou. My mush, has dirt, plaster with enamel color, bits and pieces of dry tall grass and roots. Applied to all the tracks, some darker pigments sprinkled on it and splattered with airbrush.
Finally started my filtering technique.. Not sure if this is the pro and correct way, but it works for me and gives a real sense of dirt and other stains to my model. 
1) Add very small dots of artist oils all over on side. In this case I use some colors similar to the cammo and lighter colors on top and darker on lower parts. I use very few with reds and greens
2) With a small moisted flat brush pull the paint down, colors will mix by themselves. Dont worry, initially looks like a mess.
3) Just clean the brush, and keep pulling down, use some turpentine very lightly. Apply less and less force on the hand when pulling.
4) Not bad!! ehh... 
oils are very forigiving, if you dont like it, just clean it up and start over. In my case I wanted more "white" stains and make the German cross look like fading and. So added more white here and there.
5) Now pull down again, I like the different stains..and how it looks like. It has to be subtle, your eye can perceive that the color is not all flat and dirt, dust and even dove poop stained it.
6) Finally I use a clean, dry big flat aribrush and just lighty I mean LIGHTLY even everything by pulling down and sideways, it takes out that "down" painting.
7) Here it is!
I did the same on the front of the turret, the left side is treated while the right is just clean. The change in color is subtle but gives some sense of dirt and use.
Hope it is useful for some of you.
Hugo 