Shure RK 143 G

I bought this as a replacement for my trusted SM58. However, within WEEKS it started to rust. I don't think I have a particularly acidic saliva, as far as I know, and the rehearsal room where I leave the microphone is weather-proof and dry all year round, so I'm surprised the item has started to rust. All I can think is that the quality, as with most things these days, has gone downhill. It's a disappointment, seen as its ridiculously expensive for what it is. I won't buy the brand again.