Toyota Repair: 1996 Previa, valve cover gasket, drive shaft

Question
After driving our van smells like burning oil and we have black soot around tailpipe.  It has approx. 110,000 miles.  We recently had the equiv. of a 15k servicing and replaced the headerpipe (exhaust, pipe assy).  The dealer also recommended replacing the SAD shaft because a worn rubber bushing is causing vibration (very expensive). Is the soot around the tailpipe a problem? Could the worn rubber bushing in the SAD shaft be causing?  Thank You!!!  

Answer
The accessory drive shaft has nothing to do with the exhaust emission.
You need to have it checked for an oil leak, a common leak is the valve cover gasket and the distributor o-ring seal, these leaks will get on the exhaust pipe and cause the burning oil smell.