Stainless can and will corrode to a point if the level of chromium is of a lower level than normally expected. You didn't mention what grade the spreaders are made from ? There are about 150 different grades and about 12-15 of them are commonly used for manufacturing everyday products. Most spreaders do not "rust" unless they are in contact with dis-similar materials like iron, steel. Maybe they were made with a different grade to cut costs, happens with far to many things now a days, nothing lasts as long as it used to, which is a proven fact !