Cantillon seepage?

I would drink it soon. I realize that when it's on it's side and actually seeping, it is probably pushing oxygen out. However, if it's that easy for the bottle to seep the seal probably isn't great and it might be being exposed to more oxygen then it would otherwise. If that's the case, it's probably best to drink it soon. Though someone might have a counter argument.

 

Uncapping and recapping is a bad idea. A simple crown cap is not intended to hold the high pressure from a beer carbonated as highly as gueuze typically is - the bottle is corked for a reason - and the seal on the bottle with the cork is almost certainly still intact. I lost quite a bit from a few bottles of Cantillon I ordered several months back. Tasted just as good as always. The risk of messing the beer up is far greater unsealing it to (inadequately) reseal it, than there is any risk that seepage has affected the beer. Drink it soon if you're worried, but it's almost certainly going to be fine.

 

Well if you need a quick way to strengthen the seal for 2 weeks you could wax dip it. Obviously not advisable for longterm cork storage, but it might solve your short term probs Also, store it cold to keep CO2 in the liquid and out of the headspace.

 

Oxidation shouldn't be an issue. If beer is leaking out, it means the pressure inside the bottle is higher than that atmosphere outside, so oxygen shouldn't be able to get in. Just throw it in your fridge upright for a couple weeks and stop worrying.