Originally Posted by Sugar Bear

Trying to get a look inside with a borescope is a good idea, I just don't know if you can on that engine.

Yes penetrant through the glow plug holes should get in to the cylinders, use plenty, BUT be certain to turn the engine over with the glow plugs out once it frees and before starting.

Patience is the key here, load it up with penetrant and walk away for a few days then put a bar on the crankshaft and tap it under light pressure. Add more penetrant and walk away until it frees.

Good luck!!!