" What I would like to know is can I just pull off the heat sink, clean off the thermal grease on the CPU contact point, apply new thermal grease and use the old thermal pad? If i cant use the old thermal pad i guess the only solution would be to buy a new heatsink from dell, which should come with a new thermal pad. Any ideas? "
yes, you can use the old thermal pad, but you will probably get better results with a new one. However, to get a new one you do NOT need to buy a new heatsink from dell, you just get a loose thermal pad.