Thank you for your interest in Sump Pumps Direct. I posed your question to Wayne tech support and received the following response.
We went to a higher grade of stainless approximately 2 + years ago � the bolts have always been stainless. In 2007 & first part of 2008 � the supplier provided non stainless bolts � this was the only time period that had an issue.
Hopefully, this answers your concerns. If you have any other questions, please let me know.