Grinding 833

Thats a rear mainshaft bearing
Number 9 in this pic.
Of course the others are going also, but slower.
If you get it soon enough you might not destroy the countershaft needle bearing surfaces.
If you wait, you will need a whole new counter gear because the bearing surfaces are machined into the inside of the ends of the shaft. Counter gear is part number 23, so you can see how expensive that would be.