Probably depends on what engine is in it. Each motor has its weak points - injectors, pump drive seals, etc. Hopefully someone on here will be able to comment on that specific motor - and it won't be too $$$$. Talk to your NH mechanics too.
I had that problem a few years ago. Thought it was likely the orings on the injectors. Had them replaced but pressure test on the fuel rail continued to leak. Turned out 2 of the injectors were leaking out through the electrical connector. We were able to block up the inlet holes in the injector and push air in to find it once the injector was out of the engine.
To keep the machine going while parts came we changed engine oil every morning.
Another tell on the fault was hard starting after it had been sitting. Must let air in while sitting. With a new set if injectors and a rocker set it has been starting and running well.
When it’s been sitting for a while have to let the electric pump run for at least twenty seconds to start once it’s warm it starts fine have ya ever heard of the common rail pump leaking through is shaft seal and getting in there some how
That 20 seconds on the electric pump was what we were doing. It was like that for a couple of years, didn't think much of it but noticed it fires right up with the new injectors.
I haven't replaced a timung gear driven pump. Our 9080 is not what is now termed common rail, the gear pump only goes to like 70psi from memory and the unit injectors make the high pressure from the camshaft. I think all 9080s would be like this.
You can get an air pressure test done on the fuel rail and injectors and look for bubbles, with the tappet cover off I could see fuel wash from the faulty injectors. The rocker gear has to be removed to get the injectors out. There are a couple of special tools involved to turn the engine and a timing pin.
I thought about the pump seal leaking when we were having trouble. I pulled the plate off below the fuel pump, it has an idler gear on the inside of it. Was able to visually inspect the area for fuel wash, but it seemed fine. I think it had an oring to seal the plate.
If you have a compressor equipped it won't be that easy.