Hi and welcome. I do not have that machine, so I don't know the answer to your question. I do know, from looking at the picture of the
tank in the box, it comes with spare o-rings. Are you making a hypothetical judgement, as in "
if the top cap gets too hot..." or is this something you have actually experienced? If the former, I wouldn't worry about it. I have 5 or 6 copies of the iJoy Limitless RDTA, a most similar design save for the postless deck, plus any number of regular style drippers, and it is not an issue in my experience. It is not impossible with tight-fitting dripper caps for the o-rings to "cement" themselves to the top cap making it hard to remove without destroying them, but this is usually cause by dry storage over time, not heat during use. In use, they'll most likely be covered in
juice which both cools them and provides lubrication. As to which material, I think I'd probably duplicate the rubber rings included rather than going to silicone, unless you can find some sold as "high temp". It is, in my experience, a useful trick to put a drop of juice on your finger and lube the rings when first building any top-cap style for the first time after a fresh wash, and to do the same with a drop of pure VG for storage.
If you have a caliper handy, and want a lesson in how to measure an o-ring to spec it, ping me back and I will be glad to help.
