Been smoked out on a 757. Air pressure seals on the engine core, apparently. Engine changed.
Sick as a dog for 3 days afterwards. Problem had been in the defects book for some time.
You could SEE the fumes when sparky came on board some 15 minutes after chocks.
Yes. The 757 has got a fumes problem history. Next time I WILL use the masks. Preety stupid not to have done it before.