Hello, I recently had a complementary inspection done to my '94 E320 wagon with 160,000 miles on it and the only suspect items were the two leaking oil cooling lines in the front bottom part of the engine and the belt tensioner. The tensioner is making a slight rattling noise when starting and during operation when something like a compressor kicks in. What happens when a tensioner completely fails and how dangerous is it for the engine? Quoted cost for the tensioner job is ~$400.