Sorry to bump this topic, but unfortunately I've had it happen again
This time a new TWSBI Eco, first inking, and with a new bottle of KWZ Foggy Green. Again I believe there's physical abrasion of the barrel by the piston when I went to flush the ink. I'll try to get some macro shots this weekend to show the tiny scratches I see through the loupe. The piston is resistant enough to moving back now that I don't think I could get it out without breaking the piston assembly (I pulled the nib & feed to finish the flush from the front with a syringe, but I'm afraid the body is done for anyway.)
Noting that there was another user earlier in this topic who had the same issue with another KWZ ink and an Eco, I'm still wondering if there's some very specific interaction between some component in some KWZ inks and the lubricant used by TWSBI. (But I also see in my ink log I've used a KWZ Dark Brown sample in an Eco without incident, and similarly KWZ Honey in a TWSBI 580AL, so it's not all KWZ inks, or at least not always.) I think I'll contact TWSBI, and if Konrad sees this thread and has any ideas that would be good to hear as well.
Edited by majolo, 09 December 2016 - 13:52.