Old timer at the parts counter saved me 3 hours of guessing on a DT466
He watched me grab a $240 injector puller and just said 'kid, that engine's got the old style cups, you need a slide hammer and 20 minutes', so I trusted him and he was right, has anyone else had a counter guy who knew more than the service manual?
The guy behind the counter at our local NAPA has bailed me out more times than I can count. One time I was chasing a no start on an old 5.9 and had the manual open, multimeter out, the whole deal. He just asked what the truck was doing, then told me to check the lift pump cam follower, which wasn't even mentioned in the book. Sure enough, it was wiped out. Those old timers have seen the same failure a hundred times, they dont need the flowchart. Manuals tell you the right way, but those guys tell you the real way.