Two thoughts come to mind. You've over filled it and excess pressure is causing a leak. Alternately the oil filter o ring is leaking. If you've used a Febi filter the o rings they supply are known to leak. Mine did and I've read from others the same.
Given the complexity of the DQ500 I'd be tempted to get the level set correctly by someone with VCDS and also run basic adaption to reset the kiss points. This will make for the smoothest changes.