Well, I'd suggest tracing the leak to stop those air bubbles and replace the filter to be on the safe side. Nowt like clean diesel to
help. Then crack an injector union loose, wrap a towel round it, and have someone crank it til you're sure that fuel is coming through. Once you're there with clean fuel at the injectors, then you're getting somewhere.
There's some o rings on the fuel filter I seem to remember. I'd start there if I was you.
Your previous
problem with it cutting out over 3k revs would doubtless be connected to this.