We have 4 Accuspread drop spreaders. 2 were purchased in 2008 and 2 in summer of 2012. All 4 are mounted on the back of JD XUV Gators.
After the second use of the 2012 spreaders we noticed rust starting on the hopper of the spreaders. The 2008 units don't have a speck of rust on them. Accuspread said it must be due to salt and high humidity and it is normal. I call BS. The 2008 units are used in the exact same conditions and there has been no problem.
The spreaders get washed after every use. Accuspread says they didn't change anything in the manufacturing process or change any materials.
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 !
I'll have to get pictures. I don't know that grade of stainless, it is not mentioned in the manual or on their website. www.accuspread.com (GT model) According to the representative they have not changed material or processes in manufacturing between our older units and the newer units.
The areas that are rusting are the faces of the spreader. No contact with anything but open air.
The most used stainless steel is 304L. 304L will not show any rust. Ask the question to what grade they are using. The grade just below 304L or just 304 will show rust staining as it's called. That is from the hardware running and eching into the SS. There are high grade SS but it's never used in production such as spreaders due to cost.
The other thing i have seen is using 304L and a poor grade SS (imports)wire during welding. Low grade wire will live splater. Thats whats you maybe seening as rust it's just the wire rusting not the hopper. It's almost $35 diffrence in US made wire and the Imports for 10lb rolls