Nagoya RB-66 rusting screws

I purchased a Nagoya RB-66 lidmount antenna mount from a seller on eBay. The product was new (not second hand used). After two weeks use, I noticed the screws had started rusting.

Dear Nagoya. The antenna mount is supposed to be used on cars. Cars are outside all year around, in all kinds of weather conditions. Why don’t you use stainless steel screws? Yes, I know they are more expensive.

I replaced the two screws and the four small hexagon socket screws (they also started to rust) with stainless steel ones so hopefully my problem is solved. But quite annoying. I think a product supposed to be used on a car should be able to handle all year weather conditions and it is quite annoying having to replace parts before being able to use the product properly.