Thats the 2 mate. Ok..if the telltale is weak it shouldnt be on those motors. In the water the stream is very good with a new pump kit with impeller...so if no blockage that is where I would focus. I assume you have done thermostats or removed them for the exercise (they should go back though) (I havent look back through the thread, but I think from memory you have done therms). Could it be as simple as the vanes going the wrong way or a gasket on back to front?

Cheers