I bought the steel ones from Brownells. They were powder coated or painted. The cast steel part had corrosion UNDER the paint and it started flaking off immediately. Since this wasn't a walnut stocked pretty rifle I ordered a red anodized one from PT&G and installed it. I am pretty confident that the anodized one won't rust- I know this doesn't help your problem but the cast steel ones from Brownells are pretty $chitty and I wouldn't start with one.
