Are the new o-rings the correct parts?
Knock on wood, Ive never had a leak from my Northstar inlet and outlet o-rings. Are you tightening the quick connects enough? Any stress on the inlet/outlet because of the plumbing being slightly out of line?
When I store the pump after the season I coat the o-rings in silicone lube and then put them in a zip lock bag and store them hanging on a wall. They dont get distorted, they dont dry out, and they are ready to go for the next season when it arrives.
-Chris