I get you point on faulty parts but your using worldpac and could have easily gotten a oem valve, which working on any german brand is pretty much parts buying 101. Either you or your customer was trying to be cheap and you paid the price.
I have to do this job and it looks horrible:( Phaeton 3.0 TDI 240 BHP 2008. similar or same engine. its going to off the road for a week I can see it now. Maybe I pay for help.. But no in suborn! Remove motor off back of EGR valve and soak in 100% isopropyl alcohol. That will clear it out in no time with a toothbrush ect Mr Muscle Oven cleaner works great also (Sodium Hydroxide) That is nasty stuff wear protection! New part was pricey and not needed I dont believe some cleaning product and elbow grease is cheaper.