just did a little edit you maybe haven't read yet
we used like 3 or 4 different pot designs on that card - that was when stummerwinter decided to build his own new pot. the "fill in" part is alu but the base is CU. that crack definitily does not come from it due to the MHZ-issues I explained some minutes earlier.
So we can rule out that this crack comes from the container itself. It must be something related to HS / DIE or HS / Pot.
I think marcus has a hint which paste works best but I can't remember atm (sitting in a hotel far away from home after a "monstrous" set of weizen )