Get a new thermal paste mate. Seriously, you buy CPU that is 100 times more expensive than the thermal paste not been able to afford a fresh paste every time you upgrade is kinda daft.
Could be like me he got all the parts and forgot to order the TIM and doesn't want to wait or pay shipping cost more than the value of the paste? In which case I say try it and see. Worst is you have to remount the cooler with new paste. Not the end of the world really is it?