I have a Pelikan M620, Place de la Concorde which I really enjoy, but for one little problem. When I post the pen, my preferred way of writing, the cap tends to slip off as I write. I'm thinking about putting a fine layer of rubber cement on the inside of the cap, to give it a tighter fit and a better grip. I think it should be no problem, because the threads on the cap are set far inside. Anyone have similar problems, or a suggestion on what to try?

Just in case anyone else has had this problem, I found a very simple and reversible solution. I placed a small piece of scotch tape inside the cap, well inside the threads (which, as I noted, are set in a bit). The cap now stays on no problem, just enough grip/tension provided by the thickness of the tape.

Clever idea, nice work.