I had a similar issue with my 2.7 tiptronic transmission after a mere 30,000 miles. Following many visits to my authorized dealer and an independent RAC report, the transmission sump was removed, the oil was replaced, and a thorough inspection of all clutches was conducted. The individuals said that they were unable to identify any deficiencies whatsoever. Although the situation has improved, it remains unsatisfactory, and I am no longer inclined to engage in further dispute with them.