I don't know if DuraCool is a flammable or not. If it is, it is illegal.

IF the compressor indeed is gone, I expect that the original conversion to r134 is what sent the compressor on its way. By only evacuating and adding a 'can" of r134 oil, there is no telling what kind of oil was in the can. Most of the r134 cans that have refrigerant AND oil contain PAG. PAG does not mix well with mineral oil.

Good luck,