Great video actually. There’s nothing like the school of hard knocks.
For all the exams I’ve written, the only questions I remember were the ones I got wrong, as it annoyed me so greatly.
Three things come to mind for that frustrating pump.
I don’t like Honda’s single bolt asymmetric clamping design on the inlet stub. Clamping forces should have symmetry.
When working with O-rings I use about a 3-power magnifying lens with the goal of really good cleanliness for the groves, surfaces, and the O-rings themselves. One speck of fluff will sink you.
Third, and maybe most importantly, what is the shaft seal sealing? The seal behind the bearing. As installed, the pressure side should be facing the pump rotor. Could that seal be seeping air into the pump?