I apologize for not updating to "post my findings here" as I promised. The gap was simply too far from the motherboard without enough pressure to make a thin layer of arctic silver a viable option. As for when you may need to replace the pads, the official recommendation is to replace the pads only if they are damaged (perhaps by removal). I specifically replaced the pads in this computer because it had overheated and I had to separate the heat pipe to replace the fans and wanted to rule out the pads too.