Is fuel cooler leaks on a 2007 Audi A4 a common problem?

Yes it is, common issue in most audis

(also in VW,Skoda,

seat) starting from 2002 year, especially in diesel engines. and it is expensive to fix in Audi

dealer. Anything between 400$-1000$, depending your face multiplier and how lucky you are. like most of audi

repair costs. Problem is that they didn't bother to design cooler and it's placement properly, they just slabbed it there on bottom of car without any protection.