Outer Limits 4x4 Board

I was just wondering how long thermostats last?

I have a 2002 Grand Vit which I think is on it's original thermostat. I'm up for changing my radiator as it has a small leak and was thinking about changing the thermostat whilst I'm at it. Now my GV doesn't overheat or show any other signs of over heating and the only time the temp gauge has risen was when doing low range driving on a 30+ deg day with my A/C on.

Should I just leave my thermostat and change it when I see signs of overheating?

Thermostats usually fail by opening early and making the engine run colder. There's no point changing it if there aren't any problems.