40C is within the temp zone for C2D, it is not excessively hot, these chips run warmish, it will not hurt the cpu.
The 82C result you got was from incorrect contact between the cpu and heatsink as you found out by "fiddling" with it. The part that concerns me is you state the pad looks alright, implying you have removed and replaced the heatsink without reapplying the thermal compound. Not good.
You'll be alright at those temps if they continue at that level when the cpu is under load (But I doubt this will be the case)
You should, as already stated, replace the compound with (preferably, AS5.) though any other 99.9% silver thermal compound will work just as well.
Be sure to check out the new instructions regarding AS5 (and other compounds) with regard to dual core chips, the "grain of rice blob" method is not recommended for dual cores, instead a "thin line" is now the go (see link)