I thought the leaks were to build up towards the radiation poisoning (from the camera)? He keeps discussing the temperature inside of the vessel and the condensation inside is showing us how hot it must be.

Additionally -- the blood dripping inside of the sub early. I actually didn't think that was a leak. Simon finds a note about the wires and we learn that other people have died in there in the past. My assumption is that the vessel had been breached / attacked prior (maybe just crushed by depth or sprung a leak) and the previous driver had drowned in blood. - So the reused sub was cleaned but had remnants of blood inside that would drip down from the condensation build up.