Well, this run isn't static. Despite the idea i had, it seems to depend on the character AND the account.
Don't get me wrong, every time i had a PvE character on one of my 2 main accounts who hadn't had a Zehtuka item (and who had never even been in that zone, but not very important), i'd make a few trips to that zone (Poisoned Outcrops) alone (no one in the group) and after the bridge, he'd always be there, without exception, and that's been the case for years. I now count 13 dropped in this area. Including the tests of the last few days.
It had become a ritual, a habit, i didn't even question whether it would work or not. And interestingly (or not...) it was always between ~40-50 runs, not on the 100th, not on the 2nd, not on the 17th, etc, always in this range. Skeptics will say it was just luck, but over more than 10 packs, nevertheless interesting to note, no? And luck can also be provoked, if that's possible.
When i posted in the topic: How did Guild Wars treat you today? I wanted to do some more tests to be sure that the farm was static and could therefore be repeated with a character as i described above and still between ~40-50 tries. In the last 2 days, i've created 6 characters, which i've run there, with 3 different accounts. But after 2 characters on the second main account, it no longer fell that way. It still fell, but after about 100 runs. I took a blank account (never used) and run a character there. I didn't get it until the 85th run, not between ~40-50. On closer inspection, the more runs you make on the same account, the greater the number of runs, with the added factor of luck, of course.
My theory is that it works with a time factor on top of everything else. When i used to do it, it was every 6 months / 1 year, no more. Here, i've pushed my luck with several characters over just 2 days. In my opinion, a test with blank account tends to suggest that the "state of the account" is also responsible for luck. It reminds me of the treasures in Nightfall. It takes a while to get something back into those chests (reset). And once you do, even if it's still luck, you'll (probably/surely) have a better drop with a newly created character who's never opened it. Not to mention that the gold in it increases over time, reaching a ceiling at some point. Once again, even if it's all down to luck, you can always put it on your side.
So now I'll have to wait and retest, if i get them again, still in the ~40-50 runs range, if I let 2-3 months go by. Let me remind you, they never fell the 1st time, nor the 5th, nor the 10th, nor before ~40-50, in the years i've been doing it, i've had 9 this way with characters who'd never had it. Those who got it, never got it a second time, even after hundreds of tries, although that doesn't mean it's impossible.
That's all there is to it. Sorry if i put myself forward too much, i was wrong. But i think that digging into these options and tests will prove interesting over time. After 6 test characters and seeing the number of cross on the sheets next to me, hundreds of runs in this area... i'm taking a break 
i can't see this area in paint anymore!
Note: Please count the number of runs in the case of tests on your side.
(about 12 hours to go and i'll create this little tutorial on Zehtuka) It's hot to get it back with the character solo and his basic armor at 10/eden lol.
