These motors have oil supply issue especially after 60K. You probably do have some cam or follower issues because of the oiling. A resolution for this is changed the oil and use 1-2 qts of trans fluid. Many of the small oil passages become clogged or restricted. Then after replacing the used parts, add some zddp sparingly with each oil change. It does not take much to plate the metal parts and enhance their longevity. 6 cars with this issue and not one has returned with this problem.