I was thinking about just removing the O-Ring in the light, allowing whatever wants to vent to vent, as waterproofness is not needed in my application.
that sounds reasonable to me
otoh, the gas that vents is hydrogen, it is flammable
maybe it would be better to know when you go into venting mode, by monitoring the tailcap
I was concerned that your approach to open the light with goggles and gloves, did not address safety concerns around inhaling vent gases, or having them ignite..
you may find that venting only happens when the battery goes below 1.2v
that might account for your prior use of High mode without venting, on fully charged cells, not sure
so far nothing you have posted is a huge red flag that would make me throw those batteries out
instead I would try to figure out if the venting was a one time thing, precipitated by a long run on high, that brought the batteries down below 1.2
again, not an expert, just my opinions
I do use eneloops, and I have run them down below 1.2 before. But the light I use has no rubber tailcap to bulge, its a twisty, and has O rings. IF the battery ever vented, Ive had no way of knowing that.
if I was you, and I had a "problem light", I would consider releasing the tailcap once in a while, especially after running on high. I would be more inclined to replace the light, than the batteries.
I still think your idea of removing the Oring is a valid option.