Is any leakage normal from this pen or any fountain pen? I've been using the cart that came with the pen (Namiki black) and I rinsed out the cap today and the water that came out was black. Should I be concerned?
Sometimes mine does.
It can be heat too. Even if you carry it nib up, there is still ink in the feed and if it heats up, especially if not full, the ink can burp out into the cap.
Mostly it happens from me dropping my EDC metro at work. I keep it in my front pocket and being in tool and die, if I lean over just right it falls out.
Sometimes the nib/feed even come out a bit and I have to push them back in. But that's an extreme case.