Got some 280x's still going for almost 3 years 24/7 temp 80 degrees 70% fan. Fans did stiffen up after about 2 years... I just spray some wd40 in them carefully when it happens and they are good as new again!
Ps. Wd40 is not recommended I belive machine oil is but... I've not had any problems so far... just made sure I didn't use too much so it would leak or get it on the gpu board.
WD is not good for high temperature operation. You need some grease like those used in the bike or car.
Grease is too thick. Standard motor oil works pretty well though, and is designed to handle MUCH higher temperatures than any computer (in working condition) will ever see.
On the other hand, any fan in bad enough shape to NEED to be relubricated isn't very long for this world as a working item. Relube is an EMERGENCY SHORT TERM measure intended to get you by 'till you can REPLACE the bad fan with a good new fan.
Avoid sleeve bearing fans (this SPECIFICALLY includes stuff like "rifle" "hydro" "permalube" etc) - they do NOT live up to their claimed MTBF due to failure in the seals intended to keep the lube in, and VERY rarely last even a year in 24/7 high-temp environments.
Stick with ball bearing - which can run for YEARS with no lube at all if you keep the dust and grime out of the bearings.
This is why I generally stick with Sapphire or Gigabyte cards - they come with Ball Bearing fans across the board AFAIK.
(Might be true for some other brands, definitely NOT true for HIS).