Hi Fernuce,
Bubbletrubble is far more patient than me
, but his tips are very good if you have the patience! I have this case and camera set up and have about 30 or so dives with it, and another 30 with another case camera combo. Your question requires a little explanation to answer properly. Your idea is sound but here's some further things to help.
My humble advice.
After lubing the O-ring and closing have a look at the O-ring to make sure it's all sealed no obvious breaches (sand grains etc) and it's not being pinched.
At the very least prior to each dive, dip the camera under water in a bucket. Some bubbles very will quickly appear and disappear as water leaves the buttons cavities, do it with an empty case to observe first time. Then there will be no more after the initial bubbles. Weigh it down and leave it for a while. If there is a leak any water will appear in the bottom most corner inside (unlikely I've never seen any),and you should see continous bubbles from the case. O-rings shouldn't let massive amounts in quickly if they fail, it should trickle in even if you do have a leak. You will have time to maybe save the situation.
When you take it diving tell your buddy / Dive master it's a new case and tell them your plan if you do see a leak on descent. DON'T jump in with your case have someone pass it to you once your in the water. As you descend watch for bubbles coming out or water in the case (very unlikely). If you see any ascend and pass it back to the boat (my Dive master suggested this process on my first dive) and go back to your dive minus the camera.
After every dive after washing/soaking for as long as possible 1 hour = good gets rid of the salt water. Remove O ring,wipe with care. Then before next dive, I get some tissue or clean cotton cloth , clean the case surface where the o-ring sits (both sides) and the O-ring. I then lightly grease the ring. I repeat the above process everytime I dive (unless I leave the case closed between dives soaking in water). Sounds long but in actual fact takes less than a few minutes to complete the entire process
After every dive, I soak my case in fresh water for as long as possible. If I'm diving again I'll leave it in the bucket for the next dive.
Search the Scuba Board Forums for a post by Reef Walker. He has some awesome info on basic case care. I also followed his instructions to remove some fine lines in the O-ring cavity with fine sandpaper, this helps prevent floods, read the article and all will make sense.
I hope this helps, any questions just ask. You have one very awesome camera.
