I just received a Pilot Custom Heritage 92 and I'm having some problems with it. The previous owner only inked it once, I've flushed like 8oz of dish soap water and 16oz of water through it (took forever) but the problem persists.

On down strokes and right strokes it writes PERFECTLY and way smoother than my Lamy Safari. However, on the up strokes and left strokes it hardly writes at all. I've attached a picture showing a comparison with the Safari:


Here's a video:


Any tips?