I guess there's two paths to lose compression - one on the outside of the prechamber the between the head and the lockring; the other on the inside of the prechamber through the injector seal and between the prechamber and injector. I'm not sure how tightly the prechamber taper sits against the boss in the head but I imagine the lockring imposes quite a force creating a seal. How that seal can come undone with just a tankful of the worst fuel ever is puzzling. Similarly I don't know how an injector seal can deteriorate over the course of one tankful.

Can you use drops of fuel between the injector and lockring then separately between the lockring and head to isolate the leak?

Sixto
93 300SD