Thanks for the words and advice guys. There are chips on the bumpers but covered over with dust and not visible in this photograph. Maybe too much dust!!
I used humbrol "German red brown"and a little flat black 80/20 for the chips. I roughly dry brushed these areas with gun metal first.
I didnt take too much care to get a perfect result, but wanted to see how it would turn out. I wont be afraid of trying this again.