Maybe this is a naive question, but if people still want to use this rocket design, why can't Orbital or Aerojet basically copy the design and build their own version stateside? They have enough in storage to breakdown and know the science pretty well at this point, and technology and metallurgy have surely advanced since the 60's to improve on the design and performance specs.
Every article I read says that we can't match the metallurgy. Why? I have no clue.
My guess as to the cause of the failure is fractures in the metal. That was the stated cause of the other failures. It makes sense since these things were stored in Siberia for 50 years. You would have below freezing temps followed by heating over the course of decades. That's a lot of expansion and contraction.
Elon mentioned in the interview at MIT that he was considering a new engine design that follows the RD-180 and NK-33 style because of efficiency. The Merlin engines have the highest thrust to weight ratio but fail in efficiency.