The fill tube has an o-ring that is replaceable. To change the 0-ring you'll have to pull the pan and release the "split fingers" on the fill tube and push it upwards. Be careful releasing the "split fingers" if they break then you'll need to get a fill tube from the dealer.
You can then take the 0-ring to an auto parts store and match it up, although if I recall correctly they are an oddball size and you may not be able to match it up close enough.
While you have the pan off you should replace the filter and pan gasket. Be sure to break open the filter to inspect for metal contamination.
My website has a "how to" for changing fluid and filter in the 01m FAQ.