I spoke too fast. While the leak doesn’t interfere with the writing, it would eventually clog the piston when the ink dries up. I wrote to the people at Twsbi to show them the leak and confess that I’ve lost the replacement parts after I moved homes. A nice chap told me he would sent it to me.
I also found the nib too dry for my liking. Luckily it is is springy enough to let me press it down to give a wetter and broader line. Now it is lovely and wet.