Put me on the list of knowing pilots who have been affected by 'fume events' and having been involved personally.
The two guys I know were both flying the 757/767 with RR engines (although it's alleged the 757 is the snag). They are both no longer employed having lost their medicals with exactly the same symptoms, which were severe respiratory problems. The large British airline involved claimed to have thoroughly checked the fleet with no fault found.
My event involved a 757 (again with Rollers) and having to return to our point of departure due to a smokey 'haze' in the cockpit and really quite a pungent, sickly-sweet, smell of burnt oil. We were on oxygen and it wasn't thick smoke but you definitely knew it was there. Doctor gave us the all clear but, again, aircraft checked with no fault found.......almost like we were making it up.
I believe this phenomena exists but it is not present 100% of the time, nor anywhere near that number, so it's a bugger of a job trying to pin down the cause. We've all heard of leaky oil seals etc but if that were the case, how come other crews on the same aircraft were not affected?
Time to switch to the 787 and packs that are not attached to engines
