All potential bonuses

100 cubes after regular zhelm turned unique, no door. 7 cubes after chaos zhelm turned unique, door. Tossed another 150 cubes after and got it around 12~13 more times. Door is listed as level 70, hence this is how I know it's the item level that makes it the prerequisite. Plus there's a screen of someone getting door on a scarlion.

As to 2nd and 3rd line primary, the chance is slim but it does exist. I'd say around 2~3%? It seems that any attributes that have different variation across rarities 01xyzn, 02xyzn, 03xyzn, are somehow linked. Or maybe it's just bad coding, I always wonder if this exists in KMS too. All rarities have a chance to obtain a unique primary trait if it exists for the existing rarity. (i.e. you can't get door at rare, I could be wrong, say at rare or epic since it only exists for unique, but you can get +9% str on a rare weapon, cuz +3% exists for rare type)

With your massive cubing, what would you have to say on the issue of

- 21% is floor up
- 21% can fluctuate back and forth from say 24/27/21

I'm guessing it's #2 since we woulda seen a lot more 18/24/27 % gear by now.