I've had a diesel pump seized on a Mercedes that had been running on central heating oil (was common in this area within the Polish community). Also had a Skoda pump front seal rot out on some chip fat mix twice. I wouldn't think petrol would damage rubber seals. One thing I have found on diesels that have been filled with petrol (which causes long crank time) is they get air in fuel when left after engine is hot. I've put this down to petrol having a lower boiling point than diesel & is boiling in the injectors. (I really don't know if this is true though).