I don't know anything about that computer, but I've been messing with o-rings in camera housings for a long time. I can tell you that the only way to REALLY inspect an o-ring is under a really bright light, preferably with a magnifier. The tiniest little crack or nick in it can make the difference. Testing it in a glass of water will only work if you have a massive leak. It's the pressure you need to properly test it.
O-rings should only be lightly lubricated and you need to use the correct type of silicone... some will cause the o-ring to swell, while others can damage the plastic in the computer itself.
It would be good if you could find out if a flooded battery compartment can damage the guts of that computer. I don't thing many computers have truly watertight battery compartments. You might be wasting your time with all of this. If you got water into the guts, it's likely pooched anyway. If this happened recently, you might consider the old rice-in-a-bag thing for a couple of days.