"The trigger guard on the pre-MK12 grip frames was designed as a built in and periodically replaceable slide buffer. By design it takes a little abuse and will begin to distort. If it's swapped out every 20K, there should be no problem. If you run hotter ammo, it might need replacing faster.
Unfortunately what we found is that the trigger guard disassembly system caused some owners stress.
Some tried to pull the trigger guard straight down for disassembly, instead of forward and then down. This caused added stress in the lock up area and grips would fail.
Some folks periodically forgot to snap the trigger guard shut during reassembly, and that allowed added slide travel and again could cause grips to crack.
For the Mk7 frame, the area where the trigger guard anchors was beefed up, and the trigger guard was slightly widened as it gets closer to the magazine release.
These upgrades eliminated a large number of the user induced frame problems, but not all.
For the Mk12 frames, the trigger guard is solid and there is no slide buffer. Also on the MK12 models, the frame insert is serial numbered, not the grip."
This sums it up nicely I think