Hey Brother Dan...
Another little item that effects the exhaust fan that happend with mine.... is: Do not have parts manual, nor do I know the names of the parts...but those with a wallas to look at should be able to follow this...
The little fan blades that turn inside the little toilet paper size tube, looking from the floor of the boat up into the bottom of the unit (yes..it is uncomfortable), .... OK.. you see them.
What happened on mine was that little "push washer nut" thing "let go" a little, causing the little fan blade gizmo to "slide down the shaft"..... which, changed the amount of air flow drastically rendering my unit un-useable due to lack of air flow.
Talking with the go-roo at the factory C-Dory gets them from, Karl I think his name is, (now he has an accent), just told me for a quick fix, simply push the blade mechanism back up the shaft, super glue it in place, being careful of not pushing the thing up too high.... Now, too high was not definable at the time, and wear goggles when you attempt to super glue upside down... I tried it. Yours may not have slid down .....yet... or as much as mine did, but be aware of this if you notice you needing to run it just a little higher....then just a little higher to keep the exhaust outside rather than inside. Sort of a slippery slop which is what happend with mine.
End result, just like you are saying Dan..... I had to avoid the lower settings, the unit made a bit more noise due to my "unbalanced" upside down super glue attempt, making the shaft a bit out of balanced. Sort of like a drive shaft on a car being out of balance.
My suggestion to Karl, particuarly fpr what we pay for these items, is to loose the push washer lock nut, thread the shaft, and use real lock nuts that are not as pron to slippage due to bouncing and vibrations. There is a lot of vibrations on the boats, particuarly when on the trailer going down the roads.