Yup. You have 2 fuel filters to check for leaks. Secondary is front of the engine and just a regular screw on, primary is usually frame mounted and has a plastic base to it with the fuel drain and water in fuel sensor you have to unplug before removing, so an oring on top and bottom. Because many new mechanics tend to over tighten filters, some guys only do the minimum 1/4 turn after contact on install and it isn’t enough to seal all the way. So look close for leaks there. Even if none noticed, grab a filter wrench and try snugging up both filters and the plastic part on the bottom of the primary. If it does it every time still you could remove and replace the orings or complete filters just to rule them out. If still an issue you need to check where the fuel line goes into the pump, that it is maintaining fuel there. Not an easy task and is one of the things Detroit changed each progression and size. Just follow the line out the secondary filter and you’ll see it. Temporarily adding an electric lift fuel pump to the line coming out of the tank to pressurize the system helps find leaks. It is a Detroit so if it aint leaking that means it’s empty- haha. But seriously ya might need to start with a bath cleaning everything off perfect to start seeing the leak. Remember the fuel before the pump is under suction so it will let air in, and not fuel leaking out. So don’t expect to see a fuel puddle as the evidence.
Idk the 08, but wrenching on the older ones till about 01 or 02 - the ddec had issues and although would seem to take programming, would have to be checked after and redone sometimes. So if you go through fuel system 100%, you might be back to this, but really doubtful the issue.
Could be the shop you took it to missed something and keep going there and they won’t get it. Series 60 is most hated and most loved Diesel engine out there- so another shop that really knows them shouldn’t be hard to find. I would suggest a different one because once a place starts hitting a wall and throwing parts at it- they won’t get it even if they are normally a good shop. NEw set of eyes on it.
