Our experience with the many new stainless steel fittings on our new boat which includfe several pieces specially fabricated for the boat is: Some parts tend to rust and some to stay very clean. Firstly we made sure all the parts were made from 316 stainless which is one of the most popular marine grades. Secondly corrosion will occur when the fabrication techniques have been a little suspect. In practise if only a little work is done with a tool like a file that is contaminated with another metal, this contamination will quickly set up localised surface corrosion. If you use a slightly abrasive cleaner you will eventually polish out the contaminants and then the part will no longer tend to rust. we have found that some of our fabrications (sten head fitting) were fine after one cleaning but our "spear" (a sheath around the pointy bit) required 4 or 5 cleanings before it stayed bright off its own accord. Unless you''ve got a galvanic cell going below the w/line you shgould be able to get s/steel cleaned so that the corrosuion tendancy ceases. Hope this helps a little.