Is the leak from the nib end of the section or the section-barrel join?
There's not a lot you can do inside the section to address this problem. I've found, in my own experience, that the Ps leak more from the nib than the Ks or earlier pens. The main thing to be 100% about is the piston seal. If there is any hint of a leak there, removing the cap could create a vacuum and draw ink into the feed, flooding it, and by extension, air behind the ink through the seal.
If it were my pen, I'd simply strip it down, give it a good clean, and reassemble with fresh seals and sealing.
The section is attached to the barrel with section sealant, most likely. This takes a bit of heat to make gooey and then the section screws off. The feed and nib then come FORWARD out of the section (this is counterintuitive).