One problem related to manifold/header/muffler/tail pipe has been reported for the 1996 Toyota 4Runner. The most recently reported issues are listed below.
Oil sludge problem. Coolant is leaking and oil sludge is building up within the manifold. It is using 2 to 3 quarts of oil on a monthly basis and smoking will badly when first cranked. Car checked by Toyota dealership and says nothing is wrong with car.