Thanks for all the replies and suggestions so far. I actually took the muffler off and disconnected all the hoses and filled the muffler with water over the galley sink to see if it leaked anywhere, epecially from the bottom but it didn't leak at all. Also the hoses all connect from the top of the muffler so if they were leaking I would be able to see it. When I re-installed the muffler I dried and cleaned the whole unit as well as the area where it screws into.
When I ran the boat again the spray came back from the same spot but the muffler and hoses were totally dry so I'm pretty sure I can rule out the muffler. I just can't think of anything else it could be though? I think I am going to try drilling a very small hole into this area just to the right or left of where the shaft log is and see if water starts coming out or to see what is behind there. I know it is not the exterior hull or bottom of the boat as that is much lower. Other than this I can't think of anything else to try?