Just an fyi I tested all the glow plugs on my SD when I first got it, they all tested fine. But when hooking them up to a battery only two actually glowed red.
All five were replaced and it started a lot better.
To clean your engine start with Gunk and a couple of brush's. You will need a few large ones and a few about the size of a tooth brush. Keep working it and re spraying the Gunk.
After you get 95% of the crud go back with Simple Green over everything. Get some Q tips and start working on the details.
Yes I am nuts but you can eat off my engine.
Step two is sealing the oil leaks that made the mess.