Another 348 gearbox takeapart...

Looking at the collapsing faces, as they progress, it gets worse faster... I'd suspect you'll be changing the shaft and gear far sooner than that bearing... It is a thrust bearing holding the gear in place, and there is very little lateral pressure on it, so those bearings would easily outlast the splines. I'd shoot for replacing the bearing, then spot welding the gear onto the shaft (you can always machine) and off you go - but then I have a spare shaft kicking about, so I'm not too worried of its lifetime...