I have always replaced the clutch release bearing and the pilot bushing for the gearbox input shaft whenever I've had the gearbox out of my BJ8 just because it is convenient to do so. I did this in March 2014 and measured the thickness of both the old clutch release bearing and the new. The new bearing thickness was 10/32" (0.3"), whereas the old one was still 9/32" (0.28") after 80,600 miles. Most of those miles were on long-distance cruises, which obviously is easier on the bearing.