Pond Pump loses its prime in an hour.. each time? see end. I did see a leak in the seal but why would it run in the first place?

Please help. I have had major issues with my pond. I thought i fixed
it by replacing a check valve that had a fish caught in it. But now
once i am able to prime the pump it turns off and loses its prime
after 1-3 hours.. I then have to fill the pump with water, shut off
all lines to build pressure and open the lines fast... then, same
thing.. you hear some gurgling and it shuts down.. My pump is 5-6
years old and has run dry many times. tried replacing the seal a year
or two ago.. Can it be that the pump is just in bad shape (i bought a
1hp replacement anyway, since it was never fast enough)? I dont think
we have any air coming in from the new check valve.. even if we did,
as long as the pond continued to run, would this air really cause the
pump to lose its prime?

oh yeah. When i turned on the pond and shut off ALL outlet valves to
build pressure, water started to stream out in a fine jet from the
pump seal.. does that make it conclusive that i need a new seal or
pump?

many thanks for anyone who can help!!!!