I assume you have disconnected the inlet hose and determined that the through hull is clear and water comes out if you lower the end below the water
line.
With only 2 inches of lift it should prime very easily. Mine is about 12 inches above the water
line so when it is working you have to give it several very quick short strokes to suck water up - but once it wets the valve surfaces it works fine.
You can remove the valve cover and refurbish the flapper rubber parts there. They may have crystallized minerals on them that are preventing a seal. Carefully check the "DRY" lever that disables the valve by holding the outlet valve open. On mine, the pin rotted through on the brass block with it stuck in the "DRY" position, disabling the
pump.
Finally, try lubricating the o-ring at the
pump shaft with a little vegetable oil. If this is leaking air, it will break the prime.
Having got it working, a couple of teaspoon fulls of vegetable oil flushed down the toilet on a regular basis will keep the rest of it working smoothly.