I had the same problem and I didn't get it seated correctly the first time. When I realized it wasn't seated correctly, I tried again. I put some fresh oil on the o-ring then put it in the hose in the correct spot. Then, I put the plastic washer below the o-ring in the hose. Then I put some fresh oil on the manifold and pushed the hose back on. The oil helped and it slipped on fairly easily.