Possibly some Update or driver is making your GPU to run a little bit hotter than normal.
If 90c is your GPU's Hot Spot then it is still well below its Maximum Operating Temperature Hot Spot of 110c.
Did something change your GPU's Fan curve or you can make your GPU fan curve more aggressive if you are running the PC 24/7 for Crypto-mining.
I doubt if the Thermal Paste or Pads are less efficient or needs to be replaced. I would believe that would occur after at least a year of running.