Firstly, can you state the mileage and year of manufacture for your car?
First point I would make is why after 3 probes and 6 visits you are putting it to this bunch of chocolates who obviously don’t know what they are doing. I'd say if they can't fix it after 2, maybe 3 visits then they are barking up the wrong tree by simply changing out probe after probe. .........unless you like that sort of thing
You don’t state the general serviceability of the car - plugs that aint been replaced for a while will not ensure a clean burn of fuel and mess up the engine running. So has the car been serviced regularly?
Also you don’t state your driving style, i.e. motorway or congested traffic.
Right now, as I see it, possible causes (likelihood in brackets)
1) Duff batch of probes supplied (less likely as VAG groups quality control is second to none)
2) Improper fitment / contamination during fitment (not impossible, but the foreman should be checking workmanship on 2nd return visit to ensure it wasn't the YTS / work experience gimp coating the probe in WD40 to help run it in the exhaust)
3) Some other contaminant destroying the probe, eg burned oil. (More likely and I’ve seen this a lot:
- Could be over-filled engine oil - has the car been serviced recently and if so how soon after service did the problem occur?
It's impossible to diagnose over the net mate, but I suspect your chuckin good money after bad with this garage and are not gettin anywhere. Ther ere dozens of reasons why the car would chuck out some oil through the blower causing this to happen so a vacuum check of the engine is necessary. I'd then be looking at compression check and the condition of turbo itself.
What is your driving style, have you thrashed the bollocks off it and expect it go on forever cos it’s German?
Give us a bit more info, i'll do what i can to help