I used to go to them with my 00 MK4 GTI. I had APR 93 Oct and an intake. I had a carbon build up problem due to the fact the Coil Packs were malfunctioning. There was a recall but not for my year GTI. So they said it was from me not using good enough gas. lol i guess Mobile 83 is bad. $2,300 later the manually cleaned the valves and problem was still there. They even chipped my Rim which i had to get resurfaced at there expense.
Read on the internet about similar issues, bought coil packs. Replaced them and ran perfect.
At another dealer i had my timing belt go which bent every exhaust valve... Thank god i had a warranty and only 70k miles. The belt was supposed to be good till 90k. I had no issues with the mods i had installed.
Moral of the story? Gunther could have blamed the mods on the car and denied me from the get go. They just were saying it was due bad gas and grandma style driving. lol
I think they just tried to milk me since i was young. Ive been to several dealers for issues with multiple cars. All have been chipped and haven't had any issues with non ECU related problems.