I have a Shinamo Nexus 8 speed on my everyday bike. It's model number SG-8R31, that's important since there are a lot of variations check Shimano online docs for details. Into my fourth year now still runs great. The manual says grease and clean every two years and I did that the first time, even ordered the special Shimano grease for it. I will probably regrease this winter not because I am worried about it, but I'm afraid I will lose the little tube. The special grease is for the shift pawls the bearings can take anything. Too thick grease on the pawls and they will stick. Other models use oil lubrication.

But then again my Schwinn Spitfire, circa 1960 has a SA three speed and still runs great. I think I took it apart once in the 70's when I was working at the LBS and had the manual available, like just to see.

I am very happy with the Nexus. Once adjusted no issues. Some people complain that it's hard to take the wheel off but I don't think so. It just runs and runs.