this is the second time I have a oil leak at the fuel shut off out put shaft. it required replacing a small o- ring. my coach is 1992 U280, 8.3 mechical.
A Cummins 8.3? Doesn't really matter which engine. O rings do go bad. And the new ULSD will make the old style O rings swell and wear out fast. Spend a few more bucks on O rings and get Viton which will last much longer. Same with fuel lines. Viton is synthetic rubber and fluoropolymer elastomer and is copyrighted by Dupont. You can also use Dyneon by 3M, a similiar material that will work just as well.