A leaking injector can build up a lot of carbon deposits that make it difficult to remove. A trick I learned with my Mercedes Sprinter diesel, was to soak the carbon deposits in carb cleaner to break up the carbon, unti it is cleaner. Once that is done, soak the stuck injector with penetrating oil (PB Blaster, Kroil, etc), loosen/remove the injector retention screw(s) and then attempt to start the engine. The compression of the piston helps to force the injector out without damaging it. Do this one injector at a time, and leave the fuel lines attached until the injector is loose to prevent fuel leakage. Clean/replace one injector, reattach the fuel lines, and move onto the next one.
Here is video of my leaking Mercedes injector
Here is video after loosening the hold down bolts and restarting
The injector came loose, and was easily removable. It still had lots of carbon to be cleaned off before I reinstalled with a new copper seal washer.
