Chuck Taylor the gun writer has one of the oldest Glocks in the country (1985 or so). His GLock 17 is used as a teaching gun at his school and gets shot a LOT. He's taken it around the world training. Last count I heard, 185,000 rounds (not 18,500, one hundred eighty-five THOUSAND rounds) with almost all original parts, basically springs and mag replacements, that's it.
He's stuck it in the Pacific Ocean for six months and nothing happened, frozen it into a block of ice doing a test in the Alaskan north (along with several other guns) and nothing happened, done all the mud/goop/dirt/sand tests, etc...... still ticking.
However, Taylor says the Springfield XD-9 is catching up to it in rounds fired and how it's holding up. Something around 10,000 rounds fired I think.
My personal G30 is stock aside from sights, and 8 or 9,000 rounds later, has no problems aside from it doesn't like Winchester White Box (hard primers).