So I have a 7.65mm Manurhin PP with a broken safety. That is for sure. What isn't is the cause.

All of my internet research shows that decocking is the likely culprit as the hammer supposedly slamming into the safety causes it to stress crack. This seems logical but then I spoke with the owner of Earl's Repair Service (he is probably one of the only guys who stock large quantities of NOS walther parts based on my research) and he told me that a weak recoil spring caused the safety to break due to excessive recoil forces being transmitted to the safety. He said that he has even heard of extractors and rear sights cracking because of this as well as slides and frames. The gun is about 80% original finish and the recoil spring looks great.

Which is the likely reason? I have no problem not using the decock feature with out also easing the hammer down manually but I am wondering about the recoil spring. His logic doesn't seem irrational but its the first time I have heard of a weak recoil spring causing other parts of a gun to break this way.

From what I recall there are two styles of safety levers with different firing pin to match each own. I bet yours has a square cut rear portion on the firing pin with a corresponding square hole in the safety. The other style is, if I remember correctly a rounded or oval shaped hole and pin. The latter is stronger.

The recoils spring explanation is plausible but the hammer dropping on the safety will break them too.

The P38 can also suffer from broken hammer drops.  I ease my hammer down with my weak hand to prevent that.