Zéfal Air Pump gauge not working The pump works, adds air to the tire but the pressure gauge does not work anymore... so I can not measure the amount of pressure for the tire... not an ideal situation.  Is anyone familiar with this pump having a valve or o-ring inside the pump that can be replaced or repaired to regain the pressure reading.  Loved the pump for 8 years or so... might be just time to replace it... Thanks
I've had something similar on my Topeak Road Morph; in fact you remind me I need to strip the gauge again.  My pump stays on the frame in all weathers.  Maybe yours does too and suffers in the same way.
What I've found is that the gauge can get muddy water in it, with enough grit to make the moving parts stick, either completely or partially (the latter cost me a tyre when I overinflated it and blew out the sidewall).  It wasn't seals that were the problem, but the spring and sliding indicator.  A good rinse and re-grease did the job for a year or so.
Even if you can't fix it and the gauge is in the head, you may be able to replace the entire head, either with an identical one (probably the best idea for portable pumps as you don't want it flapping around) or a similar one (on a track pump).  On my track pump the gauge isn't on the head but on the pump itself - it does however use a standard pressure-fitting thread so any pressure gauge of the right range would do.