Hello,
This is the "heat feeler" housing for the WRD (warm running device) on the injection pump. This is typical corrosion damage caused from no anti-freeze or old anti-freeze. Besides eating away steel parts, engine aluminum castings can also be damaged. Coolant turns acidic after a few years. Change it every two or three years. Find someone with a scrap injection pump and you probably will find a good used one. Anything is fixable, but replacing it with a good used one is most likely the least expensive and easiest way. I do not know if these are available new by themselves?