Ok...
(Edit Oldboat1 and I posted the same time.. LOL... PLEASE.... Listen to others first before my thoughts..... )
NOWHERE near a pro here, but as I read things, you said you have a hose you connected to the copper water tube to be sure everything was clear..
I'm presuming that when you did that, you had water coming out of tell tale and prop etc.. where expected?
If so, my newbie brain is wondering...
Can you take LU off, submerge it in water and turn driveshaft by hand/drill etc?
Does water come out of the pump like it should?
If hose worked fine on the water tube up and out like it should, then can you test the LU is working?
Maybe a seal or grommet or something around the impeller housing is leaking which means not enough pressure from impeller to go up the water tube?
This might not make sense, but it's just a crazy thought...
Hope it may be helpful.. LOL :noidea: