I finally had a chance to get down to my boat and take a look at the hoses.
I think MHO001080003 (Hose,Exhaust,3"x4",S,SX22,PreCut,Black,Wire 21) is a typo and should actually be 3"x14".
I found a local supplier and cost is about $20 CDN a foot. Hoping to tackle this on the weekend. I'm going to attempt to replace all of the hose, including the big 4" pieces.
Has anyone replaced the 4x17" piece that goes from the motor mount to the transom? It looks like if I remove the exhaust outlet from the rear of the boat, it should allow the hose to be easily replaced.