I agree with replacing if needed,..with that said,..there's no reason to be wasteful or stupid about it though,.. a little troubleshooting may be worth the effort sometimes,..not only that,..but you learn a little about how your "stuff" works.
* I've never had a trigger leak under pressure that wasn't an o-ring,..at least not that I can remember. The trigger I use ST-2000 has 3/8" pipe threaded into the valve of the trigger,..at least they used to,..haven't had one apart for a long time,.....but could be as simple as loose fittings.
Jeff