I own a 84 359 400 big cam III, and I have a oil leak that is coming from rocker box area, I think it only leaks when your goin down the road. I've had the truck in 2 shops this went no where, but they did get money lol
Either the rocker box gasket to head , rocker shaft o-ring and plug and rocker cover. On a engine that old I would imagine rocker shaft is leaking.
I thank if you have it cleaned up, warmed up and take the fan belts off it will show up. Stick a shop rag in the blow by tube and run it at about 1200 RPM. As mentioned rocker shaft o rings are common leakers with age. Always best to know what the leak is first. Then if you have to pull a box do them all. Replace all the rocker shaft and fuel cross over o rings. Retorque all the head bolts. If one is broke or pops you can get them out now. All new gaskets and run the over head. Good to go!
Are you positive its engine oil leaking? Sometimes diesel fuel will run down an engine and pick up grease and oil before it hits the ground.
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The fuel jumpers might be weeping also. Is the engine fitted with Jakes?
It's a old engine, the whole upper end probably needs to be done. OLD.
As old as this one is, I would agree that you are spot on with the recommended repairs, plus no matter what, I am sure it could us a tune up. Set the valves and injectors back to specs.
And because of it's age everybody and their brother has been in it at one time, mainly because it's a 855. But people will do completes and inframes and never ever change the rocker shaft seals. Same with cam bushings.
More than likely it will force oil out the dip stick tube, seen that when plugging blowby tube.
A man I worked with years ago came from a dealership. He said the two guys inframing Cummins would pull the whole water rail assembly off together and put it back on the same way. No new o-rings. Numbered all the push tubes so they went back in the same place and did not adjust anything. Just cannot make some stuff up and yes you never know what others have done.
Must be they got payed by the job and not the hour? Have to wonder if they even used a torque wrench on the head bolts and rod nuts, or just run them in with air wrench?
I knew a guy that used his impact gun as a torque wrench. He adjusted the torque by adjusting the air flow with the trigger. He swore it worked.
Sounds like where I work at, I asked where is a torque wrench I got puzzled looks like I introduced a new word. This ain't going to last long.