Dealership for warranty repair. Also hope you're using proper g12 or the dealer gonna laugh you right back out.
That's why you take $70k euro cars to a euro shop. Sorry my man.Oh...so here's the theory on what the previous mechanic did when they "repaired" the oil cooler before I purchased the car from them.
They purchased all of the parts from their local VW/Audi dealership. When the parts came in we believe he disassembled the oil cooler from the base plate. (apparently they come as one piece when you purchase) They believe he did this so that it would be easier to get the bypass valve in/out. Then he put the oil cooler in over the existing plate rather than using the new one. He may or may not have put in new gaskets. He also over tightened the cooler to the base. When he put the valve back on they don't think he used a new gasket there either. For some reason he had everything he needed for success parts wise but was lacking in other areas to complete the job.