I got two modern Sonnets, I love these very much.
But the ink, after a week or 10 days, it vaporizes (or dry up) inside the cap, all.
There are three C shape slits at the top of the cap, and I think they are the windows that vaporize the ink.
So I use a 5 ml syringe to inject some glue inside the slits.
The glue I used is the cheapest transparent one. It is transparent and can be used by a syringe.
And after it drys, it wont leave any stain like grease or oil.
I did it weeks ago and the ink stops vaporize.