This is old info, but may be pertinant. I was on a team that raced 1st gen RX-7s in SS at the Longest Day 24 hour race at Nelson Ledges in the early 80's.
In our first year, both team cars had front bearing failures within 2 laps of each other at about 18 hours. Drivers had been complaining for awhile on both cars.
The next year we changed our strategy and changed the entire strut, pads, discs, damper and bearings..all of it, at 12 hours, and of course had no further issues. We discussed the matter with Mazda at the time (they were very involved and supportive) and the spindle and bearings were upsized subsequently. I'm sure it wasn't due to us, but it might have been a supporting data point.