I haven't noticed any rust on mine, and some are now over 8 years old; others are about 3 years old. We kind of assumed they were made from stainless steel, since they didn't rust, but I'm not sure. We live in a dry climate, but they've been exposed to a lot of weather, over the years.

I wonder if they've made some kind of manufacturing change?

No way for me to tell if they are the ones that came with the kit or others I ordered last year from them. I would assume its cheap material used! I live on the coast and we have high humidity in the spring,summer morning the grass is always soaked. Maybe moisture is a issue with them. Down the line I would assume I wil have to buy SS ones like I found online from another GH brand. Thanks.