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Have found with Alfine + Nexus, if you take them apart when brand new, and properly ram the non drive side bearing cup with some waterproof grease (yamalube/lical is going fav) or even the fluro yellow shimano stuff instead of the white lithium grease they come with on the hub bearing surfaces. And a bit on the drive side ball race (the big guy). And make a point of every year just before or after winter rake the hub out and redo with either 1) Decent IGH grease, Cyclon do one thats no expensive and works well 2) ATF or car gearbox oil, hypoid type (stinks of strong dino). And they will last a pretty long time. Have come across dozens of Shimano IGH that ship bone dry, internals are basically starting to corrode as the bike comes out of the box/new.
I get about a year out of a belt drivetrain before it starts getting noisy, but that's working six days a week on it. But I literally don't have to touch it during that time. If I could afford to keep a spare drivetrain ready then I'd have no issues, but I never seem to have the money spare, so I run it until it's on its last legs, and then complain when I can't get replacements quickly enough. 😂
I love belt drive though. After over a decade on them I think I'd struggle to go back to regular chains.
If you're considering a Rohloff, I'd say try and save to get it, rather than settle for an Alfine or similar. My Alfine has been nothing but trouble on this particular bike, so I'm finally switching to a Rohloff after two years. Hopefully it'll be a much more pleasant experience.