Hello. I am having a similar issue with a 2019 MLX 409 Monsoon.  The boat throws a SPN:441 FMI:15 Bank 1 High Manifold temperature (stage 1) and a  SPN:441 FM:0.  Puts the boat in limp mode for 2 seconds and you can only see the codes on the inactive screen.  Boat never gets higher than 165 degrees. Checked everything list above as well as swapped the Manifold Temp sensors. Still throws the same code and more times each day. 
 

Any ideas on what to do next, before I take to the dealer?  6 hour round trip. Does anyone know how many Thermostats this engine has or where they are located?  Thanks. 

Pump assembly went back together under 20 min. I’m going to grab a set of allen heads for a ratchet (5/16 and 1/4) as well as a small set of sockets (9/16 is required for the arm that connects to the block). If I had those, it would have gone back together in less than 10 min. The biggest pain in the butt on the whole thing was getting the hoses connected back, which in the future I’ll probably do before I put it back on. This is the way to change the impeller if you are in my situation (really tight muffler). 

I went to trailer.com and got sealed bearings, brakes, rotors abd tires. Entire assembly. Check what available there

First time out this year ?

An axil just failed on the trailer for my 2005 Response.  The fender is riding on the tire.

I am having a hard time finding someone to fix it. It would help if I could get the parts.  Can anyone tell me how I figure out the Make & Model numbers for the correct parts?