My RS6 had a yellow check engine light come on. My independent mechanic checked the codes and found one bad exhaust temp sensor and a few other misc codes. He says that we should change both sensors and an engine drop is required. My question is (1) is an engine drop required and (2) if so, what else should be done "while you are in there". My car has 107,000 miles and is due for a timing belt. The belt shows wear and cracking so the timing belt needs to be changed regardless of the exhaust temp sensor(s). Any help would be greatly appreciated.