@elsa.mae - never seen an o-ring there...
the one I'm talking about is here (tank top cap seal, seals the top cap but isn't
on the top cap):
(from
SKU 9657221 and
SKU 9657692)
Not that adding an o-ring to the top cap would be a Bad Thing, but likely with one the cap wouldn't fully screw down (which might make it not meet the seal at the top of hte chimney) even if it's just a little too big for the space. The threads on the cap are pretty fine, and seem to sufficiently seal the outer bore to prevent leaks.
edit:/ did a bit of digging and clearly the original reload has an o-ring there, though I've not seen a clone that did and mine certainly didn't and had no spares for it. All said I'm able to get 14x1x12 (
SKU 2066604) to fit but I suspect a 13x1x11 (unfortunately I don't have any 12mm or 13mm OD to try) would do better though it would be stretched far more to get there.
edit2:/ interesting out of all the gold (discontinued included) reload rtas,
SKU 9616404 actually does have that o-ring.
Edited on 12/12/2019 at 9:00 PM. Reason: tried some o-rings to see what would fit