check the "plugs" where the swing arm was welded. look for cracks. also smell/lick the fluid and make sure it's water not brake fluid or oil or gas! Are you sure you are riding an Aprilia mate or are you riding a Buell with the new helicon motor with the fuel in Frame? lol
use a ramp and leave your bike in a stoppie and put a paper under the bike and see if the fluid drips. if not leave it in a wheelie and see if it drips find out where it's coming from I guarantee it's coming from either end. most likels from the axles