M103 valve guides
Any M103 motor with 160,000 miles is going to have valve guide wear to some signifiant degree. Doing seals alone at 160,000 miles (assuming that the guides have never been done) is like putting a Band Aid on a bleeding artery. It may buy you 10,000 to 20,000 miles of reduced consumption, but the guides will need to be done. At our shop, we rarely do valve guide seals alone on any M103 over 100,000 miles.