I've got a 1992 Grand Am with the 3300 V6, 101,000 miles. We've owned it since new, but my dad never changed the oil himself, and when he payed a shop to do it, it was at 7000 mile OCI's and they used dino oil. Well I've been driving it since about 96k miles and I know at least since then there has been a tapping noise, but only on the highway AFTER the oil has gotten hot (thinned out). This is getting to me, and I want to fix it. So first, I drained out the old oil (lots of sludge floating on the top of the pan) and I put in Castrol Syntec 10W-30. No real change, just good piece of mind. So being the adventurous young man I am I looked in the oil fill hole with a flashlight and saw tons of varnish and some sludge buildup around the valves. This leads me to believe that the lifters are clogged and not lubricating well after they warm up. I dont want to use any strong cleaner like Gunk or Rislone...anything thatll clean in "5 Minutes" because then itll clog up everything. So I figured a quart of MMO might do the trick, its been around for a long time and I've read some success stories. Can anyone provide some insight on my situation? Thanks.