Looks like you will have to follow/help on a new topic I created about watertight problem… sorry.
EDIT: I guess you saw that answer this morning (what a great system we have here 
and comforting to know that real masters are lurking when really needed), all solids are considered watertight and the need for that message apparently disappeared, I still would like to see it there…
Before I discovered that issue, I started playing with your CAD files, I found a couple naked edges in Rhino, even though the spinner Booleaned to the ‘cowl’ I saw that somehow the rear spinner plate was still in the solid. Then I saw that the tip of the nodes in the spinner’s curve of revolution caused the spinner to have a concave nose (likely does not matter) and that the spinner centerline was not on the x-axis by ~.8" so model could not left/right symmetrical. Fixing all that did not help but I did anyway. Never ended up getting cowl to Boolean with rear fuselage, not seem to be lofted from same curve I guess.
I guess none of that matters to watertight issue, just thought I would pass along those minor points…
NOW, to move on, I guess someone should make those EVR plots on the successful 25.6M simulation and then make further decisions on mesh refinements for MK4 project. 
ing for a volunteer who knows Paraview to rescue me …