I once had a 72 350SL come through the shop with a high pitched squeel when it ran. (this one had the 117 engine in it by the way) It turned out to be the timing chain had worn all the way through the rubber guide and was scraping on the guide It filled the front of the engine full of shavings Had to pull the engine and take it all apart to clean, and also did a valve job too.. Boy that was a close one.. I am sure it would have broke the chain soon and what a mess that would have been!!

Rob...