Hi, hoping somebody can advise me. I have just bought an old (1986) Merc 307D. I have read that the timing chain should be renewed every 100,000 miles. I drove the van 500 plus miles home and it pulled well and returned almost 30 to the gallon but was quite noisy and clattery. Since I have no service history with this van I am going to renew the timing chain but my local commercial Merc dealers say it is very very likely to be unnecessary as these chains hardly ever stretch or fail. Can anyone advise please?