One single magnet is not enough to catch all of the metal shavings that come off. There's a reason why there's 4 magnets in the bottom of the pan.
I highly recommend dropping the pan and replacing the magnets. I also recommend using a cork gasket that you can usually pick up from the auto parts stores for around $10. It's cleaner, easier to install and does not leak. I've had mine for 4 years, and re-used it a few times in between and not a drop comes through. And I don't have to mess with the goop!