I'm curious what evidence you have that they tried to fix it. Did you receive a refund? What did you try yourself before sending it in, anything?
FWIW I just fixed my own YLOD by putting the motherboard (ONLY!) in the oven at 400 degrees Fahrenheit, on convection mode, for 10 minutes. First I covered it in aluminum foil and cut out a rectangle exposing the CPU/GPU. I'm glad I had some thermal paste on hand before doing it, though, since the heat sinks inevitably separate from the chips when you take apart the unit.
Let me know if you'd like any more details; I'm sorry I couldn't answer your question more directly.