Yeah, IMO that filter assembly is suspect at best. I replaced mine early on for a clear horizontal auto fuel filter. Doesn't look snazzy but offers a clear visual indicator for water or lack of fuel.Wow, this one is being a pain! I would have thought for sure you would have found a weak glow plug. I like the idea of upgrading the filter though.
Maybe loosen the fuel line at the injectors one at a time to see if problem stays the same or gets worse?I am also looking at using infrared heat gun to check exhaust manifold temps at start up to see if I Can detect a difference in exhaust temp on one of the cylinders. Problem is #2 is kind of hidden behind muffler so am still kicking around how to do this since shooting the main exhaust manifold body at that point is the junction for all three cylinders.