lava80--when ur ready to use it--take and put some STP in the gearbox-the more the better, and add a little oil with it. sometimes the STP helps to slow the leak down, and the STP help's bring the seal back to life, if u don't want to try that at all. the gear box has to come off, and change the seal out for a new one.
to do that ur gonna have to stand ur mower deck on it's side, take the blades off, I don't know if u can change the seal with the gear box on-oh. never done any like these. I'm sure it would easier with it off-oh. good luck
if u want to try the other route-make sure ur vent is open for sure-it could be blocked-but for some reason ur seal dryed a little and left oil run out--we are guessing about it, till u stand it up and look.