Here are a couple of tips that I think will make building the BlueROV2 a bit easier, easier to track down leaks while less likely to introduce new leaks:
First is a change to the assembly instructions: Instead of removing 6 loctited screws and disassembling the 14 hole end cap, remove the 4 screws and 2 aluminum extension bars that hold the electronics tray in place. By removing the electronics tray you have the access you need to the penetrators while not risking damaging or adding dust to the large o-ring.
Second (and credit goes to Rusty for this) is if you find you have a leak and need to test your penetrators, use rubber stoppers (size #000 I believe) to plug the holes. They’re cheap and couldn’t be easier to use.
I’m posting these and other build tips on my blog page here: