My 21 Mark I (ID'd by smooth "V" [not inverted, I guess ex-verted] clip with round ball) always has a 1/4" ink ring about 3/4" from the tip of the nib.
I've flused and cleaned it all out 2 times and the vent hole at the blunt end of the barrel is open and clear.

Anybody have a clue?

Jack

Jack,

Just a shot in the dark, but what ink are you using, maybe that is the problem? Either that or a hairline crack in the hood, not uncommon in a 21.

Jim