due to the excesssive heat build up the board tends to flex cracking the solder connections..
all because there is not enough support for the actual pcb ...
if you are good with a soldering iron and a very small tip then worth having a go if microsoft say bugger off...
would never run a chip without a heatsink though get it too hot and its fooked if he can melt solder by letting it get that hot

would love to have a go at repairing one though