I hadn't tried that initially because it wasn't leaking on all sides, but for the sake of elimination I went ahead with that test. I made sure the lid was totally emptied of water, the hoses were drained, and there wasn't enough water in the canister to push through when sealing the lid. I reattached everything, pumped the siphon once, and waited for the water to get through. It made it to the output and held for about 15 seconds before it started leaking again. It's only leaking out of the handle closest to the disconnect valves, and it's happening whenever the pump is primed, even if it's not plugged in.Get some Vaseline and rub it liberally on the main gasket that goes around the lid. This will likely solve the issue.
Any other options to try?