the warranty only lasts 1 year
it's best you watch gilksy's ylod guide on youtube (here is part 1 of 6) - after that you can decide for yourself whether or not you want to open it (it's not that easy to get to the cooler/fan)
I think if you feel confident enough you should do it and replace the thermal paste with the Arctic Cooling MX-2 (it's easy to apply/remove, cheap, non-conductive and a high quality paste)