I think some caution is needed with this wrap-in-a-quilt and/or heat gun cure method.
It assumes the cause of the misery lays in the degraded or partly lost connection between the logicboard and the about 2 x 2 inch nVidia board, more specific, some of the leadfree solderballs in the Ball Grid Array (BGA) have failed in one way or another.
By itself, blame on (the) leadfree solderjoints is not far fetched, many electronics manufacturers had and still have to deal with those. One could say, leadfree solder is a quite different cup of tea compared to classic lead solder.
So something wrong with the leadfree solderballs is indeed a possible culprit.
However, it is NOT the only one...
There also came to light an issue with the nVidia chip(s?) itself. There are several GeForce 8600 sub-types or versions.
The nasty and prone to failure cards, were equiped with a 602-chip, the better, or should one say more robust, ones had the 603, anyway NOT a 602.
The 602-chips failed internally, as such the 603 can be seen as the redesigned, improved version of the 602.
This implies, in case of misery and the graphics-chip appears to be a 602, any solder reflow attempt like the wrap-in-a-quilt method and/or reflow and/or reball and/or heat gun or baking will not work.
And let us face it, reballing is a skilled specialists job. One could do it oneself, as long as the proper equipment is at hand.
Apple abandoned the GeForce 8600M-series with 602-chips as soon as it became clear what went wrong and moved tot 603 and later. The Apple logicboards exchanged via the extended warranty program are/were all 603-chip equiped.
With greetings from continental Europe
Feike Hoogenbos