I have a 2001 SeaRay Express Cruiser. Engine replaced in 2007 with 5.0 MPI Mercruiser crate engine. The manifolds and risers have not been changed since. Boat is trailered and gets flushed with fresh water upon each use. Is the replacement of manifolds and risers a DIY? I have read up on some of the posts on the subject, seems like the concern is the bolt snapping. How do I prevent this, and if I can, what are the remedies?