A few pointers from a very old electronics professional. (me).
1. DO NOT bake it upside down. Gravity will pull away the parts you wanted to fix (IE the GPU core and capacitors) and actually make the situation worse if it goes again.
Lay the foil dull side up on a cookie sheet and put the card on it bottom side down so that none of the components fall off when baking. Wrap up some heavy coins in a roll of foil and place them on the main GPU and ramdac. These are the two things that are causing the failure and when not the card is done. pressure is what is needed. What caused your problem in the first place was expanding/contraction of the fibreglass PCB board. Without pressure you will form 'hourglass' shaped solder connections and they will simply fail again. Do not put foil balls under the card as this will cause small components to fall off. You've had it if that happens.
2. Get some liquid flux and spray it over the solder contacts you can see and under the GPU and RAMDAC as best you can. Solder does not deteriorate (yours should still be lead) but flux does. It's basically acid filled epoxy resin and heat causes it to become brittle and crack.
3. Replace all of your thermal pads with very slightly thicker ones and either shim or put a dense thermal paste onto the main GPU. The reason? Well, as I said, what caused your failure was warping of the PCB as it heats up and cools down. You ideally want to apply as much pressure back on them once repaired as possible. This will prolong the life of the card. If not? Well, failure rate within 90 days is about 80% likely going from a massive thread I read about it.
All of the above worked for me.