The 130kt speed restriction is an advisory from Sikorsky based on cruise torque settings. All the foot cracks have occurred either in Canada or the North Sea. PHI in the GOM, who has 50k hours on S-92s have always flown at a slightly lower torque setting to achieve 130-140 knots airspeed and has never had a foot crack.
In 200,000+ S-92 hours, the foot crack phenomenon is relatively recent. Sikorsky is examining casting and manufactiring tehniques to establish what may have changed. There is a planned solution which involves using a new lower gearbox casting which is being trialled and will be retrofitted to all S-92s as it becomes available. It is based on the stronger casting of the Canadian MHP program, stonger because its a 30,000lb aircraft.