the VRMs get a LOT hotter than people realize. when i was overvolting my 5870 my VRMs were nearing 120c.
that one VRM probably just doesn't have optimal contact with the thermal tape. if it bothers you, you can apply some TIM or just try reseating the HS.
they are designed to run at those extremes though, so they should be fine.
Just make sure there is a thermal pad that is making contact then you should be fine but as for life span that may be the one thing about this generation that will cause problems. The 3870x2 had very hot running VRM and would have failures then the 4890 had the same issues besides cooling for the gpu core. Just be sure to clean it once a month and you should be fine.
You could always replace the pads with thicker more gooey pads for better contact but you may still see up to 100c at times of load. You can always dump a fan near the read end of the cards for extra air flow. As for mods I know a few tricks but most people get into trouble when they decide to go aftermarket cooling.