ARP offers a few levels of studs with various torque yields, depending on the material used there are definitely instances where 1 grade will hold better than another. When you're dealing with the performance and pressure levels most are looking for in 996 performance you've got to look beyond "Standard" ARP and into their Custom Age and L19 materials, and larger head sizes as well when possible. In many other applications we've tested this and changed and implemented/developed different studs for the application in one of these materials, it sounds like Evo tested and had to do similar for the 996/997.

In this case it was likely the hose, the o-rings get worn when removing the hoses to drop the engine, and most shops won't replace them when doing so. It's always a good idea to replace the o-rings on any coolant hoses when removing and re-installing them, cheap insurance to prevent a nice scare like this from happening.