If it hiccups at idle it probably was run on veggie at one time.To attack one problem at a time as a weekend task it might not seem so bad. Nothen better sounding than a happpy 617.Oil leaks come with all diesels and age ,the diesel engine will outlast any gasser .The 617 is an exceptional diesel known to go 600k with most of its orig. parts such as the injection pump ,you cant say that about internation 7.3 or cummins 5.9.The best advice is to get it on a rack for inspection .Not sure about the turbo issue ,describe whats going on here.