But I am also a tinkerer, and I enjoy experimenting. So, I tried to use a small Kaweco Sport Demonstrator as eyedropper pen.
That is a particularly well-suited pen for this transformation: a cartridge/converter of reduced size, all plastic made, and transparent. Then, I proceeded to fill the whole barrel with ink. I did not apply any grease nor added any gasket to the thread. And it does not leak at all. The nib I chose is a 1.1 mm italic from the Kaweco Calligraphy set.
Two sets of threads can be seen on the demonstrator pen. The one on the left is for the cap. The one on the far right is to attach barrel and section. This thread seals the barrel tightly--no ink leak after days of carrying the pen around in my pocket.
The result is a very well behaved pen—a generous flow, a big ink deposit (about 2.5 ml of ink, versus 0.7 ml in a short international cartridge), and an interesting nib. The drawback, of course, is being bound to use this royal blue ink for quite some time.