Hi Sean
sometimes it is necessary to cover the stainless steel capillary tube to try to prevent corrosion caused by chlorine. This can be necessary in certain enviroments such as swimming pools , where fish are stored (sea water) etc . I have seen a number of these T2 valve which have lost the charge due what is termed as deep crevice corrosion.
What product is stored close to the valve .?.
The blackening of the brass body is indicative of an aggressive enviroment