without the use of sulfites your open to any and all infections. my guess is that the synthetic cork has things sealed up slowing everything down and your getting a bit of a reduction reaction along with the alcohol being converted to vinager... give it time, sealed the way it is slows things down so much... in another six months to a year try it again.... and remember the normal proportion of olive oil to vinegar is two to one if all works out good for that you might consider pulling a few corks and putting in a sprig of fresh tarragon some other nice herb and recorking.
i've been making wine for over 35 years and i never suggest beginners try making wine without sulfites all too much to go wrong. i'd give a beginners odds for making a good long lived wine about this: flip a coin... heads you get vinegar, tails you get vinegar... if it lands on its edge you get good wine!!!
mike