My first thought is that your dealer is banking bux for the future. IMO, there's absolutely no reason that an input shaft should be required at 100k.
On my '90 K75RT I did replace the clutch at about 95k. There was nothing "wrong" with it (or the input shaft), I just did it as a preventative exercise. You should really not need a new clutch plate then either, unless, like me, it just makes you feel better. Or, for some reason, you're really hard on them.
I would, at the first sign of difficult downshifting, grease the input splines. Unless, you'll feel better knowing they've been recently lubed, then go ahead and lube them.
Just my two cents,
Tom