Brake Fluid Storage Oddity. Any chemists in here?

[kbcons]

After changing out my car's brake fluid, I wanted to store the leftovers for a short time to add if necessary. Because brake fluid is hygroscopic, I attempted to store the partial container of it by slowly flowing CO2 into the top of the container. The CO2, being heaver than air, should have displaced the air which should simply spill out the top. I then sealed the can tightly and left it in my garage overnight. The next day, I found the can crushed, as seen below. Temp at time of sealing was in the mid 80s (F). Overnight temp in the mid 70s (F). Back to the mid 80s (F) the next day.

• Pentosin DOT 4 LV. Can is steel, 1 liter.
  Estimate about 30% filled with brake fluid.
  Brake fluid chemical makeup:
  Triethyleneglycol monomethylether
  2,2 -(octylimino)bisethanol

Did I run into an unexpected endothermic reaction?

Thanks!

Ken...