Along the same thoughts as Stu .... the pump may have developed a bit of 'bypass' and therefore cant develop enough 'suction' to prime itself ... this loss of 'prime' wont happen when the hose isnt removed so that air cant enter the pump.
Rx: -- So, attach the hose to the pump, hold the open end of the hose HIGHER than the pump and completely fill the hose with water, etc. when the hose is totally filled, HOLD YOUR THUMB over the open end and then QUICKLY put the open end of the hose into the bucket and then start the engine, etc. The 'priming method' as outlined above should allow you to suck in all the AF you need.
Another poster recommended for you to check the side clearances of the pump body plate vs. impeller, etc. .... do so when you get a chance.