If it's not leaking bad, it's really it's more of an annoyance then anything else. As long as you are conscious of the leaking and know that you have a limited amount of time in a pond, it's not a terrible thing. If you are planning on staying on the water for any extended period of time I would change the bearings first. A bilge pump is a quick and cheap way to at least have a little peace of mind if you don't already have one.
Other than the increased risk of sinking, your chains, sprockets and inner bearings will also get wet which can lead to rust and faster wear on those parts but even with a leak-free machine, mine usually ends up covered from splashing mud and water anyways.