It's still around in cocaine. Being added to bricks before they even leave South America. I believe there's a test kit out there that uses bovine alkaline phosphatase, and you can always do things like send your coke to Energy Control or DanceSafe.
Levamisole doesn't have a direct effect on thinning your septum out... putting acidic vasoconstrictors like cocaine up there is what does it. Not saying that levamisole is safe (it fucks with your white blood cells) but it won't help or hurt your septum.
If you're worried about your septum thinning, make sure to moderate your use of cocaine to less than once a week if at all possible, carry saline nasal rinse to wash your nose out afterwards, and avoid using any sort of decongestants (especially anything you spray in your nose) or anything else that could irritate your nasal tissue. Your septum gets damaged because cocaine reduces the blood flow to tissue that it contacts. This is why it's still used in nasal surgery... it doubles as a painkiller and something to stop bleeding. But if you do it a lot, then the tissue in your nose ends up not getting enough oxygen or removing waste products effectively, and the cells will die.
You want to encourage blood to flow through your nasal tissue as much as possible, and the easiest way to do that is by not doing cocaine all the time