Hi Joe, from the description of the problem I'd have to lean towards gravity and no backflow system being the cause of the leaking (just a guess though). If it were me, I'd wait a week, fire it up again and see what happens... let it run for 5-10 minutes (unless there is a large amout of gas spewing out). Then after another week (more time for any trapped gas to evaporte) fire it up again and see what happens. If it's still leaking gas, I'd go to a Toro dealer and have them check it out.
Anyway, not an expert opinion... but my 2 cents worths.