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Frankly it doesn't need an o-ring groove at all - I thought it was going to be mounted in a box but the requirements changed and I don't need to shield it anymore. But I designed it so I'm sticking with it, ha.
That sounds like a good thing to try, though. I'm printing the whole thing 'on end' but I think you might still be right, it could possibly support itself. I'm going to use the PVA though, cos we have a roll and it's really satisfying to use!
You might find that you don't need support for the o-ring groove if you print slowly enough with a fan?