Yes they are durable. This is why the injection pumps are sometimes the last thing to suspect. Sounds like you are slowly getting there. I totally agree being on the same page is very important as well as you mention.

I assumed you were just slightly loosening the nut at the injector and getting a dribble. Never considered a hard line totally off. Sorry.

I might try running the engine on straight diesel to see how it does. Maybe you have. The diesels thinner viscosity can sometimes indicate something.

If it will run on it then pretty certain the injection pump will tolerate a real internal soaking cleanout. You could be processing fats in there into the delivery valves causing upsets.

People have reported gobs of stuff coming out their relief valve port after injection pump soakings. Kind of a crap shoot but at the same time has fixed issues many times. Otherwise you risk being in a vicious circle situation. At the same time it may not be this at all.

My thoughts go back to people that have purchased WVO burning cars in the past. If those cars had engine issues I used to recommend cleaning out the fuel system first. At least unlike many people in the past that did conversions. You know how things work and seem to know what you are doing.

Did you consider that you might not be changing your oil often enough? There is a chance that chain tensioner got gummed up with wvo component in the oil. What you described about it was unusual. Just something I would think about. It could be something else that caused it not to function.