I have a mid-1990s vintage Rotring 600 fountain pen with F nib that I love. The cap on this pen has always required a bit of a twist to get it to "lock" after capping it. Over the years, the cap has become looser, and today I noticed that when I cap it (after the twist), it pops back open again (and shoots the cap across the desk, in fact). It no longer stays capped. It appears the brass in either the cap has loosened, or the nubs on the barrel that lock into the receivers on the cap have worn down. I don't see anything up in the cap.
Is there any repair for this?
*EDIT - I just got it closed. But it's a pretty tenuous hold.