Input shaft - life left or replace?

I used to put the highest-sitting brass on Second, cuz I always wore that one out first, lol. First gear gets the lowest-sitting cuz the rpm differential is only whatever your idle-speed is, say 750 rpm, and I don't like first gear to work too good, as it just makes engaging it more difficult. Whereas at 7000 rpm, the rpm differential averages 2000ish rpm, so the brass is really gonna have to be tip-top to get the job done in a reasonable period of time.
I finally gave up waiting, and slick-shifted second and third. Now the trans, at WOT, doesn't even know the brass is still in there, the sliders just overpower them as fast as I can throw my short-stick. Yet when granny-shifting, there they are, good lil soldier-boys that they are.
As to the slider-hubs, yeah sometimes with higher mileage units, the splines have to be back-cut as well, and the sharp edges knocked off; and if the struts have left tracks, or are baggy, then it's time to retire the hubs.

But, if you recall, I have a GVod being used as a splitter, so some of the time, at WOT, I don't even shift into second cuz, First-over hits 60@6400; 7000 will get me ~68mph
and I rarely even get into third gear, cuz 6200 in Second-over is around 93 mph, which is what my car does in the Eighth, lol.
So I don't feel the need to go any faster, lol.

BTW
Some of the later overdrives had the hubs cast in a different configuration and it is not possible for them to be rotated relative to the sliders as there are no adjacent detents for the struts to engage. So then, those can only be assembled in one specific way, namely, with the struts engaging the detents..