Dream Buster wrote
So now we know that breathing visible toxic oil fumes can not cause ill health in COMMERCIAL aircraft crews.
I didn't see that. I just saw that the evidence supplied couldn't prove it (as opposed to observing a relationship.) Answer: find the right evidence.
It's like saying smoking causes cancer. It doesn't, more than 95% of smokers do not develop lung cancer. BUT 90% of lung cancers occur in smokers. So there is a relationship but not a proof of cause from the effect.