Just completed my 10k service using Castrol edge and gen Audi parts, including fuel filter (£60!!!!!!).
I decided to clean the EGR valve, thinking with 130k miles it'd be clogged up. However when I removed the connectors, I was surprised to see the valve virtually spotless !!!!
What I did find however was the plastic manifold from the engine to the valve was heavily deposited. I whipped this off and removed about a tennis ball amount of build up !!! (wish I'd worn gloves!!!)
I also checked the flapper valve motors and connecting rods, both worked perfectly and there was no movement/vibrating of the rods like some people have experienced.
I think the problems people get are down to how these diesels are driven, too many short journeys and not revved enough. Obviously people like to keep the revs down for economy but in the long run it ends up costing you more in parts. Taking it up to high revs a couple of times a week clears deposits and keeps everything working as it should.
Same with the flapper valves, they seem to fluctuate more at low revs, so obviously they'll wear quicker with that style of driving. Getting a couple of mpg more doesn't make up for a ££££ repair bill.
Just my thoughts.