well dex cool has a rusty look its orange colored could just be old turns brown is not a bad thing ,but yes sounds like a good flush in order,i know it cost more to have someone do it ,but you can do it yourself cheaper if its got black junk in it i would think about radiator change there like $60,00 an the res tank like $30.00 unless its just a little if there is black gunk on the end of the res dip stick meens your rad is full of it or could be ,if not you should be good with a change only ,anything to keep it looking good ,that was the one thing about mine is when you look in there all you see are the aluminum insides no gunk built up there or nothing ,an stay with the dex cool i do the 100% then mix it with distilled water 50-50 ,is cheaper walmart ,dont run it to much with crapy anti freeze get that right first ,dont put green in it,i am sure Gorn can say more about that