Ensure all the pump bolts are removed....I made the mistake of removing one of the timing chaine cover bolts thinking it was the pump bolt. my car's pump was really corroded and was fused to the engine block. it took numerous hammer hits to get it to break free. the trick was using a tool slim enough to get between the pump and engine block.
was there any pitting of the metal where the o ring seals? were all the pump bolts securely tightened? was there any debris on the o ring mating surface? did the o ring tear when it was stretched to install on the water pump? defective water pump?....I recently purchased two, brand new fuel pumps for another vehicle/project and both pumps were defective.