I am not sure what the new drop rate is since the last change, but it was supposedly improved. Whether that's a 1% improvement or 15% improvement I don't know. I am not sure if that # is available in the data files to view.
Based on a 33% drop rate it will take about 404 runs on average to get your helm, but you might get some other rare drops along the way. If you ransack it solo that would be roughly 50 weeks on average. If you run with 5 others and ransack it would take 8-9 weeks on average assuming nobody else needs it. With rerolls, a fully party and discovery potions you can obviously shorten that to most likely one day. You can always have above average or below average luck which makes that better or worse.
Here is the math which hasn't yet been updated for the recent drop rate improvement, because I have no data or verification on that yet:
https://docs.google.com/spreadsheets/d/16IE7hwZVYJ4ihbfpPyxIew3FfBfgT4bCI8xpHi6n-Wk/edit?usp=sharing
Just running the content regularly with dual boxes and/or friends I've had quite a few rare things for me drop that I wasn't even looking for, but might be useful at some point. My approach is that I won't farm for a specific rare, but if it happens to drop for me I will consider it in my gearing.
But definitely don't farm for a broken item with no timeline for resolution.
To answer one of your questions, yes you can run a level 30 in the heroic wilderness to get those rares and there is no penalty to do so. If you or your friends have the free saltmarsh vip potions that can improve the heroic drop rates also. Just bring a bank iconic alt or new character with the potion. Obviously the ideal is one level 30 and 5 iconic looters with saltmarsh potions with different people needing different items from those rares.