Try pulling the injectors. It take 10 minutes to take out or put back.
Take them to a Diesel shop to service them. It'll cost you $60 ea.
If you need any parts tell them not to fix but sell you new ones.
They cost about $90 each new.
I tell them to test them and if they think they need any parts just stop there.
I did it to my engine and it started like it was a new Yanmar!