I would locate a 5/16" hex rod & drill prime it CCW. I like to smooth the hex where it goes thru the bushing area & wrap some tape around it CW. If no go as you said take off & fill the filter. Still no go pull the filter & put a bag over the filter mount & drill prime again. Still no go pull the pump & pour oil into the block passage going down to the pickup & retry. Not sure if you can add oil to the output passage but do it if you can