I bought a Fisher Space Pen with a PR4 black medium cartridge some months ago. It's been leaking for some time, and seems to be getting worse - every time I use it I have to clean off the tip or get big splotches on the paper which take a long time to dry. It seems the leakage is actually not at the tip but at the seam between the blank tip and the copper-coloured main part of the cartridge. I carry the pen in a trouser pocket and live in a temperate climate, so I guess the temperature of the pen could get up to almost body temperature and down to night-time room temperatures (10-15°C) daily. Are there any tricks to avoid or stop leakage in such cartridges?
I don't know how hack-y this is, but leaking is not a normal part of the wear and tear of this pen; it is a manufacturer's defect. You should send it back to the manufacture. Fisher Space Pens are warrantied against any malfunction basically forever.
Fisher Space Pen > Repair or Replacement
The operating temperature is from −30 to 250 °F (−35 to 120 °C), so your not even close to being out of spec. The ink is forced out by compressed nitrogen at a pressure of nearly 35 psi (240 kPa), so I don't think any home repair or kludgey workaround is going to work with this pen specifically.
PVA glue along the seems may help and is also easy to remove if required.