Well, I want to purge out the old gas, so I'll likely be leaving the system intact until I run at least 30L through. I don't think the line is BLOCKED, just restricted. Although I would be more inclined to think that the FPR didn't like sitting, doing nothing for two years.

When the pump primes, pressure shoots up to like 55psi and then backs off to 43.5psi before cranking. So I think the FPR knows what pressure to get to and is able to get it there, but there's something slowing the fuel's return to the tank. With the pump running constantly, the FPR is doing its best but can't drop the pressure low enough.

Once the old fuel gets flushed through, I'll pull apart the FPR and dig the filter out. I think I remember opening the filter and cleaning the element, but that was back before Christmas.