I have done a few Audi/VW's that have had petrol and they generally are fine if you get it flushed well.

However, we had a guy with a Touareg R50 with only 6000km's on it, he completely fucked his. Was filling up from a tank of diesel he had on his farm, done 10 tanks and on the 11th he got the dregs at the bottom, had diesel bug in it and water. Car was running rough and cutting out, we told him not to drive it and get it recovered and he took it on a 300km road trip.... 10 new injectors, 2 new fuel pumps etc etc, ended up costing the guy around $25k NZD.

Car is now for sale through us at $150,000NZD he paid $195,000 just 8 months ago, so he lost $70k in 8 months.....