(I posted something similar to this query on the repair board and received no replies, so perhaps someone here has information to share.) I have a Sonnet (Mark 1 series) with a nib I have never liked, and am thinking of having it reground. But I have some concerns about investing in a pen with a pressure cap, i.e., a cap that snaps on and off. Most of my pens have screw caps, which I think are more secure. So, my question is how likely is it that the Sonnet cap will become too loose with age? And, if it does, could that be repaired?

I've got one pen with a pressure cap that tends to come loose, and that pen is a Lamy Safari. It started doing this after about five years of use. I have several Sonnets, up to 8 years old, and none of them have this problem. I also have some pens with screw caps that come off rather easily when carried in a pocket. So I don't think you can predict from the cap type whether you are going to have problems or not, although I certainly understand your concern.

For what it's worth, I seldom carry pens clipped to a shirt pocket now. The Kaweco Sports that I always have in a jeans pocket are in a two-pen case. The Rotring 600 that is always with me stays clipped to the pen sheath in my RoadWired cell phone case, on my belt. Any other pens that I have with me for trips or meetings are in a leather pen case (2-, 3-, or 4-pen) in my briefcase. No worries.

I'm not a long time Sonnet user, but I think the cap closing gripper is more robust than a Safari, etc. I think they should have a good long life, and I bet there are parts out there to fix if the grippers do weaken...