I'm just stating that I consider a Series 5 Gitzo indestructable unless you abuse it some how.
Gitzo now have a series for in water use, I have used mine in shallow waters also sea water, hard to avoid in Denmark, no problem.
And it is not related to how you used or 'tested' any smaller Gitzo series tripod... I can easily 'test' a Sachtler and it would never erect again...
I find a lot of twist in the smaller of the Sachtler designs, with the thin diameter sinle legs extended, quite obviusly not designed for big lens photography when fully extended.