Hi Darran, another option for rust is hydrofluoric acid 2 to 5% strength, or if you know any stainless steel fabricators near you they use a pickling paste for cleaning welds which is produced from hydrofluoric acid it usually comes in a 1 liter tub with applicator brush, just brush it onto the rust stain and let it dwell for 5 minutes agitate with a scrub brush and give the whole area a good rinse as its nasty stuff. Tadgh