There is something very fascinating about this "fumes" thread. I have no experience with the Boeing 757 but I did spend the better part of 20 years on the BAe146.
I have to say that I never ever, ever had a problem in all of that time. I am now happily retired and find myself in the rudest of health. I did however meet a few pilots who were (apparently) affected by the phenomenon but never while flying with me as I recall. (Running the packs in full cold before putting the APU air on might have helped).
Now I know FAStoat and I have no doubt that what he is saying is quite true and he is not the only pilot that I have met who has blamed fumes for their ongoing problems.
So why is it that the rest of us don't have a problem? That is what the aviation medics should be investigating.
Perhaps my wartime upbringing of lots of cod liver oil and concentrated orange juice set me up for a healthy life!