Grab your handy dandy sanitizer and get 'er cleaned out, sure you'll have some minor exposure to oxygen but as long as your not violently stirring or shaking your keg you can just CO2 purge the container. I've done this several times with no problems, once I realized I reversed the posts so I just got a small bucket of sanitizer took everything apart, switched posts, threw on some lube and put it all back together. The other time I was unsatisfied with the way my beer was tasting so I dry hopped in it, but then I had some clogs so I had to take it apart. Just remember to sanitize everything, including your arms(if you're going that deep), and you'll be fine. Just my opinion, no lost batches so far.