Short term, the answer is easy. Taste it. Oxidized wines taste .. stale. They tend to be discolored (brown-ish rather than red, and white wines tend to look wan and yellow). If you are lucky they may taste a bit like sherry. Longer term I would argue that even if it is oxidized you may not be able to detect any flawed flavors rightaway but you may taste them after a year or two. But this is sort of a worse case scenario. A poor seal is not the same as a foot of headroom in a carboy that has been aging for months and months. How long has the wine been under this "bad seal"? How long has it been since active fermentation ended? If you are talking about a few weeks I would happily assume that there is plenty of CO2 still blanketing the wine. If you rack onto K-meta then you have inhibited oxidation... and if this is still actively fermenting then your anxiety is TOTALLY misplaced. I ferment in buckets loosely covered with a towel and that means absolutely no seal whatsoever. Bottom line? My money is on everything being fine.
A leaky stopper; two weeks... Others with far more experience in this than I do may have a very different opinion but I would taste the wine you have and if it does not taste "stale" and does not look "discolored" then I would relax. In my opinion, oxidation is analogous - in many ways - to rust. You expose bare metal to moisture and the metal bonds with oxygen and you get rust.. but rust does not happen overnight and a few molecules of metal -oxide cannot be readily detected.. But let's say you look at the wine and you see that it is discolored (in 2 weeks that would be miraculous, but that's another story) or it tastes stale.. You can always use some for cooking; add mulling spices to some, and make a batch of vinegar from the remainder.