Ah crap, Fermenter has an air leak!

Currently 5 days in to fermentation of a 1.100 beer (North Coast Old Stock Ale Clone) and I realized that my vittle vault fermenter has a leak in the lid seam somewhere. I realized this when I put some pressure on the side of the fermenter, and I heard air escape the side rather than through the blow off tube. I was suspicious of this before because I haven't had much (if any) airlock activity before in this fermenter.

My question is, should I rack the beer off of this fermenter into a container that is not structurally compromised? This beer is going to have a really long primary fermentation (3-5 weeks) and I don't want to compromise it when it stops making enough CO2 to keep positive pressure from outside elements.

Obviously strict sanitary procedures, minimizing oxidation, etc would be practiced.

While it is in active fermentation, leave it be. The CO2 will keep infection risk next to nothing. Once it slows the you can rack it to another vessel to finish and bulk age.

What's a good point to consider it "slowed"? My version of that might be different than another's. I'm thinking, after the krausen has fallen?

That's what I would go with ... let the krausen fall and then move it. And when you siphon I'd be aggressive and pick up some of the trub to ensure I had enough yeast moved over to clean things up.